Additional hard drive in inspiron 5490 series.

Technically, no - a hard drive is a 2.5" device that this system will not support.

It is possible to have two M.2 SSDs.  Manual has the details:

https://www.dell.com/support/home/en-us/product-support/product/inspiron-14-5490-laptop/docs

Welcome to the Dell Community @RKSHREE 

The information on this laptop is still not clear.

Have you tried removing the Base Cover yet???

Inspiron 5490 Service Manual:

https://www.dell.com/support/manuals/en-us/inspiron-14-5490-laptop/inspiron-5490-service-manual/removing-the-base-cover?guid=guid-2af521fd-af5c-4b87-9b35-377d963f32fe&lang=en-us

I do not understand where two M.2 SSD's would mount???

There is an option for an Intel Optane with SSD combo card???

Now the strange thing is that there is an SSD/HDD ZIF connector just above the battery.

There is no mention of it in the manual???

That's why I ask if you have removed the Base Cover yet???

Best regards,

U2