https://code.tutsplus.com/tutorials/quick-tip-how-to-work-with-github-and-multiple-accounts—net-22574

1. create a new SSH key
ssh-keygen -t rss -C “your-email-address”

save file as id_rsa_WHATEVER into ~/.ssh folder

2. attach the new key to GitHub account online
retrieve public key from ~/.ssh/id_rsa_WHATEVER.pub
paste it into github “ssh public keys” section

3. tell ssh about the new key
ssh-add ~/.ssh/id_rsa_WHATEVER

if successful, response of “Identity Added”

4. Create a config file
touch ~/.ssh/config
vim config

paste the following into file

#Default GitHub
Host github.com
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa
Host github-WHATEVER
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa_WHATEVER

5. Try it out
git init
git commit -am “first commit”

login to WHATEVER account, create a new repository named “hello”
git remote add origin git@github-WHATEVER:GitHubUsername/hello.git
git push origin master