RPG Insanity

Is there a way to return in the past after finishing the game?? Im looking for the portal that teleports you in the past but it seems to be nowhere. Cuz i missed a lot of sub quest especially the quest that will reward me the demon call ring which i need for grinding.

Heya! I haven't played this game for a long time, but If i remember correctly you can return to the past via a teleporter in the dark lord tomb(?) The same room where the dark crystal seal thingy is broken early in the game.