Hi,
To reset the login name of a technician account, login as an administrator or a different technician who has admin privilege in ServiceDesk Plus (You cannot edit and make changes to account with which you have logged into ServiceDesk Plus). Now go to Admin > Technician > edit your technician account > go to login details > select the option 'Remove Login' and save the account. Now edit the account once again, provide the new login details, generate the API Key and save the account. Check if that resolves your issue.