As a former Finnish citizen, you can apply for Finnish citizenship by submitting a citizenship declaration. Read more about citizenship declarations.

However, you cannot regain Finnish citizenship by declaration if you lost it because you gave false information in your earlier citizenship application and received your citizenship on wrongful grounds.

You also cannot regain Finnish citizenship by declaration if you lost it because of the annulment of paternity.

No, you will not lose your Finnish citizenship in that case. Finnish legislation allows multiple citizenship (dual citizenship).

Please note that if you hold another citizenship in addition to your Finnish citizenship, you will not necessarily retain your Finnish citizenship automatically when your turn 22. Read more about retaining Finnish citizenship at the age of 22.