Step 1) The old MIC will need to be disabled by taking the battery out of it. Then try another NEW MIC RESYNC
Step 2) If the NEW MIC RESYNC still doesn’t hold after completing Step 1, then unplug the DCA on the base. Wait 1-1.5 hours, then plug the DCA back in and try a NEW MIC RESYNC again.
This typically works like a charm.