1. Log in to any node in the ceph cluster.

2. Use "ceph -s" command to find which monitor is out of quorum.

3. Remove that monitor. $hostname is the hostname of the monitor not in the quorum.

ceph orch daemon rm mon.$hostname --force

4. Check if the monitor is back to quorum. If it is not back, do the following steps.

5. dd the monitor container service. 

ceph orch daemon add mon $hostname

5. Add monitor back to quorum. $ip is the public IP address of the host.

ceph mon add $hostname $ip

6. Check if the monitor is working and back to quorum.