I am certainly no expert on this, but my understanding is that the open source Mesa drivers (for AMD graphics) are installed by default in Linux. You shouldn't need to do anything. Are you saying it's not working?
EDIT: let me add a link to an article that talks about updating those Mesa drivers. Again, I'm not on Linux, so this is just from old knowledge and searching:
https://itsfoss.com/install-mesa-ubuntu/
