Maintenance for the week of May 18:
• NA megaservers for maintenance – May 18, 4:00AM EDT (8:00 UTC) - 9:00AM EDT (13:00 UTC)
• EU megaservers for maintenance – May 18, 8:00 UTC (4:00AM EDT) - 13:00 UTC (9:00AM 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".