Cancelling a request, and access before maturity

There are two different moments, and they work differently:

Before the deposit is placed — tell your adviser and the request is withdrawn. Nothing has left your balance and nothing has been opened yet, so there is nothing to unwind.

After the deposit is placed — the term is fixed. That is exactly what the rate pays for: the bank knows it has the money for the agreed period, and prices it accordingly. Early access, where it is possible at all, is a matter for the bank that holds the account, and the conditions of that specific offer govern it. Speak to your adviser before assuming it is available.

This is the main practical difference between a fixed-term deposit and your platform balance: your balance is liquid, a fixed term is not.