If you enter a wrong code three times, the radio locks you out for 1 hour. In 2021, patience is your only calculator here. Leave the ignition on (key turn) for 60 minutes exactly. Do not turn it off or the timer resets.
In 2021, finding a completely free "instant" calculator for the RCD 310 is rare due to the way Blaupunkt encrypted their later serial numbers. However, you can try: blaupunkt rcd 310 code calculator 2021