Compressing music files to fit a given size [closed]

I have a few thousand mp3 files on my pc of different quality (total 10gb). I'd like to compress all of them to fit my smart watch which has 4gb storage.

Are there any tools to compress all of them using the total size of all the files as a target?

Aside from 'product requests' being off-topic…

You're kind of asking for a tool no-one really wants. Compressing an entire library to a specific size, especially with such a massive data reduction, is just not common-enough for people to really want it ^[1]. There's also the issue that to achieve this, you first have to recompress them all & see where you end up, rinse & repeat until it fits. You can't really guess what will happen in such detail with an mp3 until you do it, or at least do part of it & extrapolate.

You didn't specify the more important data-points [existing bit-rates & number of files], so we'll have to guess.
If your files are all 320kbps, then 128 will still be absolutely fine for a portable device^[2] [so much so that most people would literally not be able to tell the difference], but if they're already at 128, then no-one's really going to want them at 1/3 of that size. You could get away with 96k mono & get somewhere close, but tbh, I'd just pick fewer tunes.
How long are you going to be listening? 6 weeks?

^[1] … or sensible enough for anyone to consider making it ;)

^[2] If you're in the Apple ecosystem, there's already a simple check box in iTunes or the newer 'Music' app that will do this on the fly for you at each sync. There's also an option to just "fill the device with a random selection"