If you have an SSH config file, you can retrieve your Host alias from there and use the following command ,say, to clone your repository:
git clone git@github-{your alias name here}:username/projectname.git
For example, with the following SSH config:
Host github-azizkale
HostName github.com
User git
IdentityFile ~/.ssh/azizkale
Your command would be:
git clone git@github-azizkale:azizkale/projectname.git
Make sure:
1- Your SSH key is created and stored at ~/.ssh/azizkale.
2- The public key (azizkale.pub) has been added to your GitHub account under Settings > SSH and GPG keys.