You can't move a booking to another time or court in the app. Either cancel it and book again, or ask your club. Refunds outside the club's cancellation rules are also the club's decision.
Moving a booking
Do it yourself: cancel the booking (you get the refund shown in the app) and book the new time.
Ask the club: only the club can move a booking to another time or court without cancelling it.
Refunds outside the rules
Within the club's rules, the app refunds you automatically when you cancel. For anything else, ask your club directly, for example:
a refund after the cancellation deadline
a refund for a session you couldn't attend
a refund for a membership or club wallet
Why Nettla can't decide
Nettla provides the booking app the club uses. The money for your booking goes to the club, so only the club can decide on refunds, cancellations and moves.
Good to know
Find the club's rules at checkout under Cancellation and other policies, or in your confirmation email. See "Where can I find a club's cancellation policy?".
To contact the club, see "How do I contact my club?".