Tap the core features on the homepage or in settings to view you current Set & Spend requests.
On your current request tap edit.
You will see the amount you have already requested which you can edit in the input area.
You will be asked to review when this is available, if you want it to repeat and confirm the edit to the request.
You can delete your request by tapping the bin icon in the top right of the edit screen.
If your request is available immediately and you have already spent some of it, you will only be able to cancel the request for the remaining, unspent amount. This will be clearly visible to you in-app.