Jul 20, 2020, 16:3707/20/20
I don't think you directly can.
I'm not sure if this applies to Tag Team arena too- but in Classic arena, teams get unranked after a month of inactivity. I bet it would also apply to Tag Team, so maybe if you don't participate in Tag Team for a month that may be the way to remove your defense from Tag Team.
Why would you want to remove your defense in the first place, anyway?