It is all written here in Github docs.
Check or edit config file: cat ~/.ssh/config which looks like this:
# github/terviseabc Host github.com-terviseabc HostName github.com IdentityFile ~/.ssh/terviseabc_id_rsa
Generate keys.
ssh-keygen -f terviseabc_id_rsa
This is how I clone the repository from github:
git clone git@github.com-terviseabc:terviseabc/terviseabc.dev.git
How to use multiple SSH keys: https://www.youtube.com/watch?v=N2hMGEeYR7c
How to change your committer name.