I just got a free mount skill change coupon so I manage to use that item. However, I couldn't find any button at the stable keeper to use that item. Could anyone help me to fix this problem on the newest look of bdo please? Thankyou 

Hello, Galloran!

This might be the case of the UI not fitting properly with your screen resolution. Try changing the screen resolution, as well as scaling down the UI and see if this will make the button visible.

If this does not resolve your issue, you may send a ticket so we can help you further.