Hari You'll want to read these instructions on how to make locally uploaded extensions function with Flarum. It may be slightly dated but should still work.
You don't have to clone from github, just make sure you upload the extension files in that instruction.
I'm not sure about the composer update command at the end, there is a way to call composer from php but it isn't supported on all shared hosts. You may have to use the terminal for that.
