Most of the time you don’t need to change the XenServer pool master but if need to do maintenance it will require you to move the pool master to another host.
Make sure HA is disabled before proceeding if you are using it. This can be done via xencenter.
Find the UUID of the host you want to nominate as the new pool master
Use this command to set the new pool master with the UUID from step 2
xe pool-designate-new-master host-uuid=<uuid>
Re-enable HA if needed. This can be done via xencenter as well.