I am an English speaker, and the Indonesian course is supposed to come out in a couple of years. So I chose to start learning English for Indonesian speakers (to learn Indonesian)!
It is context based. Also you can use time words like "kemarin", "tahun lalu" or (depending on what you want to say) even "sudah". It's hard at first for indo-European speakers to get the no past tense but with time it is very easy and natural
If you have other Indonesian questions feel free to ask me. Give examples too