What exactly do you mean by "credit"?
Cash credit? Membership plan? Add-ons?
If it's cash credit and you want to use it to buy stuff (e.g. membership) then the option to pay using the cash credit should appear automatically at checkout if the amount of cash credit is at greater than or equal to the amount being charged.
If it's not then you'll have to add more cash credit to increase the cash credit balance first.
Is you're referring to membership or add-ons then these should just work automatically.
If necessary please clarify further what exactly you're trying to do and having a problem with.
If you need to contact 48 support about this then see the links in my signature below.
