If you burnt the track to a 'data CD' (which can hold documents, images, videos, music file, etc) the it will almost certainly
already be in MP3 format. (A data CD can be accessed from your computer but, even if it's only got music tracks on it, won't play in most CD players).
If you burnt the track to an 'audio CD' (similar to the CD's you can buy in shops) then all of the tracks on that CD will have been merged into a single file on it. To extract a single track out from it (in MP3 format) you need to 'rip' the CD:
https://www.easytechguides.com/rip-a-cd-in-windows.html