How do I become legal resident of Puerto Rico

My husband & I have been in PR for 3 years & are curious what we need to become legal residents & be able to vote here. Is there certain form to fill out & can it be done online? I have to straighten out our taxes as well as we didn't get last $500 each for pandemic & IRS didn't let us add it to our taxes. If anyone can explain process of filing income tax in PR please post here. My husband receives a pension from USPS & was wondering if he should be paying income tax on it.