Maintenance for the week of April 20:
• [COMPLETE] NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• [COMPLETE] EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
Go to your Collections by pressing U and you can select your current mount from there.
If you do not know how - you select "mounts" from the collections panel and then the mount category - hover with your mouse over the mount you want to use and press "E".