It’s tricky but I’ve done it.
Save a Krita brush .bundle file in your downloads folder. The full path is usually
/storage/emulated/0/Download
In Krita, go to
Settings > Manage Resources > Import Resources
When you hit “import resources,” take a good look at the file manager. I’ve heard that not every Android tablet handles this in the same way. There should be a dropdown menu at the top that you can open and look for the path that leads to the download folder - it ends in emulated/0. Pick that one and then the downloads folder should show up and allow you to select the bundle.
The reason I say this is tricky, is sometimes it is very difficult to get to the download folder. Android has not made it easy for apps to access other sections of the device storage.