How to switch standby to master on postgresql 13?

For High Availability on DB was build Active-Standby(replica) cluster on Postgresql-13. Inserting data correctly transfer to 'replica' server, it is ok. Now, I want check case, how i can make change roles on two servers. for this I the /var/lib/postgresql/13/main/standby.signal was delete, also for apply changes restarted postgrsql.service Something tells me what I'm doing wrong. So,

1. how to make a master out of a replica,
2. how then from the old master (which was temporarily not available) to make the master back, without losing data?

Sorry for my English.