In case you already have a registered Stocard account where all your cards are saved, you can log into this existing account in your Stocard settings under "Account". Now, please choose to "Log into another account" (iOS) or "Switch to another account" (Android) and select the login method you chose when you registered your account.
Please note that logging into a different Stocard account will reset all cards that are currently stored in your Stocard app and replace them with those cards that are currently stored in your account instead!