If you have registered a public ssh key to your GitHub enterprise account, you could side-step the issue using an ssh url
cd /path/to/repo
git remote set-url origin git@github.ibm.com:WBurney/Blockchain_SDO.git
Then any command like git push/git fetch/git pull/git ls-remote would use the SSH URL set by git remote set-url.
But regarding your original issue, try and follow “Creating a personal access token for the command line”.
If you are on Mac, update your credentials from the OSX Keychain.
You might need to remove an old cached credential first.
(As commented by RayLoveless)