The First Homes scheme will apply to the home forever (subject to limited exceptions), meaning each future buyer and the local community will continue to benefit from it every time the property is sold.
This means that if you are ready to move on, you must notify the local authority and when selling your home you must apply the same discount to market value that you received on your purchase, and only sell to buyers that have been approved by the local authority as meeting the First Homes Eligibility Criteria (including any local eligibility criteria set by the local authority at that point in time). Your solicitor/conveyancer will run through the full details with you.