So, to become a legislator, you need to become a citizen first. You can do that here: The South Pacific. As a citizen, you will have the right to vote and run in elections for Delegate and Prime Minister, as well as serve as an appointed Cabinet Minister or High Court Justice.
Then, once your citizenship application is approved, you can apply to become a legislator here: Office of Legislator Applications. That will give you the right to vote on legislation and run for Chair of the Assembly.
Hope helpful, and please feel free to ask if you have any questions!