You need to be a Snoop Plus user to access this feature…
To do this, all you need to do is tap on the 'Spending' section on the nav bar, then tap on the 'Personalise' option. You’ll then be able to setup your payday in the app inline with your pay cycle frequency. This will then sync all the features to your pay cycle, as opposed to calendar month.
Once set up, you can delete or edit the existing pay cycle whenever you like.
Snoop Plus is available for £4.99/month or £39.99/year.