Immediately change your Facebook account password to a strong and unique one, review account activity and look for any suspicious login locations, unfamiliar devices, or unauthorized changes to your account information, enable Two-Factor Authentication (2FA), run a reputable antivirus or anti-malware scan on the devices you use to access Facebook, remove any suspicious or unfamiliar applications that may have access to your account, report the issue to Facebook through their Help Center or Support page, let your friends know about the situation so they can be cautious about any unusual friend requests or messages they might receive from your account.