The easiest way would be for your global admin to add themselves to the group as an owner long enough to create the team and then leave that group. Otherwise, the current group owner will need to be added to whichever security group has been whitelisted to create Teams.
You could possibly do it via Powershell. Using New-Team -GroupId <String> command. This will add Teams to existing group. Not 100% on if it allows global admins to run this against a group they don't own, but worth a shot.