After arriving back in Imperia for the games in Caltha, there will be a Ship Captain located on the beaches. You can pay him a fee and he will take you back to the previous regions you have visited. This is the only way to return to these regions and complete any games that you did not earlier in the game. He appears at random times, so enter and exit Trikata until you see him. The fees are 20,000D for Nordagh, 20,000D for Steppes, and 15,000D for Expanse.