You steam something to return it to its previously warm state. This is when you go to reheat something. But we usually use it to talk about bringing something up again and again in conversations or arguments. That's why it means to rehash or to bring up again. You're bringing up memories from the past and steaming them up again.
The reading comes from 蒸れる and 返す. Combine this knowledge to reheat your memories.
There you go again. Girls always bring up old issues. I don’t want to deal with that.