It looks like the CoolerMaster AIO would fit. The radiator is the same dimensions as the Corsair Hydro Series H60 (2018) 

We just went through an AIO replacement for an Aurora R11 . . . in this thread 

It would be an identical replacement for your R7 if you also decide to run a push/pull configuration, which is optional. Read through that thread, then come back here to work through your AIO upgrade.

you would need to remove the R7 Dell backplate before you can install non-Dell AIO cooler such as the coolermaster one which uses its own backplate.

then you need to see whether the coolermaster radiator can be mounted in the same way as Dell rad. the CM rad appears to be larger than Dell.  not sure if it would fit the Dell case.  

also the Dell cooler liquid pump is low profile whereas the CM is tall.  not sure if the R7 swing arm psu would let you fit a tall pump in there.

for procedure to remove Dell R7/6 cooler. refer to AW vdeo

https://www.youtube.com/watch?v=RtZo4w4lTE0

for tips on removing Dell backplate refer to https://www.dell.com/community/Alienware-Desktops/Aurora-R7-CPU-air-cooling-upgrades/td-p/6136442

The Corsair AIO cooler can use dell backplate and its M3 screw, as validated by user updating XPS 8940 cooler to Corsair without need to remove dell motherboard and change backplate. https://www.dell.com/community/XPS-Desktops/Can-a-Corsair-H60-or-80-be-installed-in-a-non-K-configuration/m-p/8235370

I am not sure about the coolermaster backplate compatibility with Dell M3.  

on a different note, no need to get rgb liquid pump in R7 because visual of pump is blocked by psu when case is closed.

Nevermind I figured it out. Just had to screw them out for a while 

So I am currently working on removing the radiator but the 4 screws on top of it won’t come out. I have removed it before and haven’t had this issue. What do I do?

So I have removed the motherboard and the cpu from the socket so that I can change the backplate but the screws to remove the stock backboard don’t unscrew at all. Is there a specific screw driver I need for these to unscrew?

You probably did not need to do that at all.

Did you get the CoolerMaster AIO or Corsair or other?

Does it look like this

I had to put in the new backplate to be able to put in the cpu cooler. Installation and everything is fine and got everything plugged in. Now when I start my computer I get no signal from my monitors. The fans are spinning and the cooler seems to be working fine but I don’t know if I messed something up in computer. I’ve restarted my pc a few times and still no signal so I definitely messed something up. Im thinking that when I put the cpu cooler on I was not able to put the cpu cage with the level around it because the new backplate didn’t have holes for the screws so I couldn’t put it on. Or maybe that’s how it’s supposed to be and maybe I plugged something in wrong. Anyone know how to trouble boot this issues?

What AIO CPU cooler did you install? Regardless . . . you probably did not need to change the back plate (too late now). If you did not install the CPU bracket, that will be a problem.

Drop some photos of the inside of your case so we can see what you've got going on.

Re:  I was not able to put the cpu cage (ILM) with the lever around it because the new backplate didn’t have holes for the screws so I couldn’t put it on.

I think you probably used torx screw driver to uninstall the three screws holding the Dell backplate to back of motherboard.  And the new back plate has no place to hold those screws, thus you have no ILM (Independent Loading Mechanism) for the cpu now.  the most critical watch out is lga1151 socket pin.  A bent pin can potentially brick the board.

R7 Dell backplategeneric ILM

So I put back in the original backboard and put the cpu case thing back on this time and re applied the thermal paste. And when I boot up still no singal to the monitors. Here’s what the inside looks like 

It is a little dark up top, but it looks like you have the radiator fan connected to TOP_FAN and the pump power connected to CPU_FAN. Try connecting the pump power to PUMP_FAN mobo header. Make sure all of your RAM and your graphics card is fully seated and locked in the slot. Put a light on and drop more close-up photos (it's free)

in a no POST scenario, remove discrete gpu, use the onboard Display port (#4) for video.  remove all usb and storage devices from motherboard.  remove all RAM and install only one memory.  hope you did not remove cpu from socket.

replace cmos battery with a brand new CR2032 and try clear cmos settings on motherboard jumper (#14).

OK . . . good job!

Now what is she doing when you try to power up?