1. If your current pool master server is online, you need to connect to it by ssh.
Before changing the pool master you have to disable the HA feature temporarily.
Next, get the list of your current servers in the pool.
Get the uuid of the slave you want to make the new master and type in the command:
xe pool-designate-new-master host-uuid=<new-master-uuid>
2. If your pool master is already down for some reason, you can still make any slave as master of the pool.
Issue the following commands from the slave that will become the new master:
xe pool-emergency-transition-to-master xe pool-recover-slaves
Good luck with the new xen master 🙂