Any possible profit or loss that you made when selling crypto-holdings in the P.F.C. app needs to be declared to the Swedish Tax Agency (Skatteverket) with your annual Income tax return (inkomstdeklaration).
Only owning investments in cryptocurrency does not need to be declared, even if these have had increases or decreases in value.
Questions about how you declare should be addressed directly to the Swedish Tax Agency (Skatteverket).
HERE you can find more information about how to declare the sale of cryptocurrency holdings (in Swedish).