You have two choices, either you direct ask for internet packages at the shop and they will sell you what they have, which can sometime bbe problematic as a 6GB package can be 2GB Internet + 2GB Local internet (usable only in the area you buy it) and 2GB of streaming data.
What i do to be sure of what i'am buying is i just top up with normal credit (Pulsa biasa in bahasa indonesia) and then convert the topup into package i buy either true USSD codes (like *363# ) or, for a more user friendly experience, through the MyTelkomsel Application on my smartphone.