In Hebrew, the term translated as remember does not always mean "to recall something forgotten," especially when God is the one remembering (see study notes on 8:2 and 32:36). Here, it means that God would keep his promises to the patriarchs by doing what he said.
Asking God to remember is more than making him aware of a need. It is a plea for him to act and meet that need (compare Luke 23:42–43).