Couple of issues can be there to block you from accessing your github repo and throwing 403 error. Hence please go step by step.
Step-1 : Local git is corrupted or not working
git branch -r [If it gives result you are good]
git ls-remote --heads <remot_git_location>
if one of the above is working then your local git is good. If not use
git config --global --unset credential.helper
Step-2 : From your IDE (IntelliJ or Android Studio etc) see git is configured and test it.
Go to Default Settings-->GitHub and Your host should be "https://github.com"
Get your Github personal token. Login to your github account from browser. Settings -> Developer settings -> Personal access tokens.
o Select all “repo”, gist and “read.org” in your scope.
o Create the token
Last step: If still not working, Go to VCS--> GIT --> Remotes --> Change the repo to include token explicitly
https://user_name:<your_TOKEN>@github.com/reponame.git
Paste the token in your IDE and test the connection.
If your problem still persists then check if there is network issue.