You’d normally do it here:
But the badges do not have titles assigned yet, I mean hardly any do. I feel this will be added eventually. Some titles may not even be related to the badges and assigned to the account.
If a badge has a title associated with it, you’ll see it while viewing the badge (far right):
Also, just noticed this for the first time:
Not sure if it was present before or I’ve been ignoring it absentmindedly.