If you have bought a local SIM card and you are out of phone or data credit, you will need to top it up. You can do so in every little supermarket in Bali (Indomaret, Circle K, Alphamart, MiniMarket, …).
You will just need to give your local phone number to the cashier and the amount you want to add or the package you want to buy.
If you are in a more remote area, you can simply go in any little shop and ask the tenants to add credit for you. This is very common in Bali as most locals use prepaid SIM cards as well.
If you do not have a local SIM card yet, you can read our article “Where to buy a SIM card in Bali?“.