How to slim down .git folder?

I have a repo that I've just uploaded to codeberg. In earlier versions, I had a ton of media files - they have now been removed. However, when I uploaded the repo to codeberg, I'm getting this notification:

Your private repo uses up a large amount of disk storage, while all content should ideally be public and licensed under an OSI- or FSF-approved Free Software licence. Please refer to our ToS and the FAQ about software licenses and private repositories. Thank you for considering to release this repo to the public or reducing your required disk space for this repo.

Turns out, my pushed files are 1 MB, but the .git folder is 279 MB - how do I slim it down?