Changing a regular court booking into a match or vice versa in not possible in Nettla as of today. This is due to the different rules and settings that exist in the two different booking types, such as 'pay your part', 'level spans', and 'gender exclusivity' that may not affect one type but does affect the other.
Is there a work-around solution?
Yes, you can simply cancel the existing court booking or match, without refund, and the register the same player(s) as Paid on the other booking type as that you want the original session to change into.