Disconnecting an integration from Marker.io is usually as simple as clicking the "disconnect" button in your integration admin
Unfortunately, Github requires an extra step
When you wish to disconnect your GitHub account from Marker.io, GitHub requires that you also revoke Authorized OAuth Apps in your GitHub admin
Step 1: Disconnect GitHub inside Marker.io
Disconnect your GitHub account in Marker.io here:
Step 2: Revoke Marker.io access inside Github
Log into your GitHub account and go to your applications settings and revoke the Marker.io app here:
You should now be able to connect a new GitHub account.