Phrases Phrases for Making Reservations

I need to amend my existing reservation...

Meaning

To change an existing reservation.

Translation language

John: I need to speak to someone about my booking.
Alice: Certainly, sir. What can I help you with?
John: <b>I need to amend my existing reservation</b>. I need to change the time.
Alice: No problem. Let me just check your details. So you need to <b>amend your existing reservation</b>.