Repairing the stairs or other structures in Family Island requires specific resources and sometimes a certain level or quest completion to unlock the repair option. If you're unable to repair the stairs, it's likely because you have not yet met one or more of these requirements. Gathering the necessary resources, levelling up, and completing any prerequisite quests will eventually allow you to undertake repairs and restore access to previously unreachable areas of the island. Read: Family Island Free Energy Link