I have a work GitHub account and a personal one. First I used the personal one for test projects, then I moved on and did a repository with the other account on the same com
I have found a temporary solution in which first run killall ssh-agent then add the ssh keys generated for the account you need to use ssh-add ~/.ssh/id_4shameer
This is the one way in which we can work on the multiple github account when we will get the error of type ERROR: Permission to user/repo-git.git denied to username.