Exit from "Not Synchronising" Primary Database in availibility Group

Hi I Create an availibility Group with a primary and a secondary. (For test)Then run Planed Failover.Switched to secondary. That's ok.After that I update some tables on secondary (That now is primary)I Run Again Planed Failover on server 2. Switched. OKBut primary database Get (Not synchronising) Status.And in primary I dont have that updates.How to sync these databases and exit from Not synchrionysing. Thank you