Go to the slave server that you want to use as pool master.
First disable HA on your XenServer Pool.
Now list UUID for all the hosts
To designate a slave XenServer as the new pool master
# xe pool-designate-new-master host-uuid=("enter UUID number - without quotes"
If your pool master is down or unavailable, log in to a slave XenServer and enter the command below.
Nopw you need to re-establish all connections to the slaves from the new pool master.
# xe pool-recover-slaves