German phrase
Ich möchte auf ~ umbuchen.
Meaning
I'd like to reschedule for ___
When to use it
It asks to move a booking. This polite wording suits appointments and other formal arrangements.
Example dialogue
Ich möchte auf einen späteren Termin umbuchen.
I would like to reschedule for a later appointment.
Wann würde es Ihnen passen?
When would suit you?