There must be a million utilities to do this (try searching “linux mass rename”), including ones that allow you to rename media files based on their metadata… each works in different ways, so you’ll have to look yourself for one that fits you (personally, I like the ones who open a text editor with the file names and you just edit them).

If you use KDE (DK about other environments) and only need a progressive counter, the simplest way is just select the files in dolphin, hit F2 and enter a pattern like “Tv Show Episode S01E##.mp4”.

(of course you can also write a script to rename the files, but I guess you wouldn’t have asked if you were prepared to do so)