Welcome to the Dell Community @Jhors 

If there is not an "Eject" button then it is most likely a dust cove plate.

Go to "This PC"

There if you have a DVD/CD it should be listed???

If one is listed right click on it then click on "Eject"

Best regards,

U2

Please list Dell model number and version of windows. Example: Dell Inspiron 3543, windows 10

If you don't know, type msinfo32 into the search box, you'll see it listed by System Model.  

@Jhors 

Have you ever used the drive before???

To better assist you, we would need the exact model number of your laptop/desktop???

Identify your Dell:

https://www.dell.com/support/contents/us/en/04/category/product-support/self-support-knowledgebase/l...

Best regards,

U2

PLEASE DO NOT POST ANY SERVICE TAGS!!!

Even if optical drives don't have an actual Eject button, they typically have a manual eject pinhole.  If you unbend a paper clip, you should be able to press that into the pinhole to activate the manual eject.  Afterward you can just remove the disc and close the tray, and the optical drive will continue working normally.

@jphughan 

@I cannot see any pinhole where I can insert a paperclip

Type Device Manager onto the search box then look to see if DVD/ CD- Rom drives listed. If there's one, expand, right click driver and then update it. If there no DVD/ CD driver, select 'Action' at the device manager taskbar, and then click on 'Scan For Hardware Changes', hopefully DVD / CD drive appear. Please click on link below for additional DVD / CD troubleshooting.

Your CD or DVD drive is not recognized by Windows or other programs

https://support.microsoft.com/en-us/help/314060/your-cd-or-dvd-drive-is-not-recognized-by-windows-or-other-programs

UCAMEB4ME I forgot to tell that I've never used the CD Drive. 

@Jhors 

Try removing the Optical-Drive Filler: "One screw"

Inspiron 15 3531 Service Manual:

https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15-3531-laptop_service%20manual_en-us.pdf

Removing the Optical-Drive Filler starts on page 17.

Regards,

U2