The password can be reset by text message but this option must be enabled earlier.
To be able to reset your password via SMS, you must have a Polish mobile phone number.
Therefore, open Moja PG portal, click My account and then My data. There you should see a suitable form. The change these data you will need to confirm them with current password:
When the form submitted, the authorization code will be send to the mobile phone. This code should be entered in next step of the activation process.