From your Home timeline, navigate to your menu bar and select Notifications. Then go to your Mentions tab.
Find the post in which you’re mentioned that you wish to untag yourself.
Tap or click on the more icon.
Select Leave this conversation.
You'll receive a prompt that lets you know people can't mention you again in this conversation and you won’t receive further notifications. To proceed, select Leave.
Once you leave the conversation, your username (or “handle”) link will be hidden.