They aren't doing that, they are going to, with the cooperation of the new license holder, continue listening on the previous frequencies until those collars run low on battery¹ and start using collars that operate on a different license.

¹ at which point a device on the collar causes it to fall off

This must be so annoying to the animals. Humans catch you, wrestle you to the ground and put this random object around your neck that you can't get off. It must be such a relief when the battery finally dies. I understand it must be done, but it must be annoying never the less.