Short Answer : You cannot recover.
Authenticator Plus encrypts your data using your master password as input (cryptographic key), without master password we cannot open decrypt your data.
For security reasons, master password is never transmitted outside your phone/tablet, due to this master password cannot be recovered. If you have any unencrypted backup as html or text file you can reimport it
What do I do?
Setup the Authenticator Plus with new master password and setup all your accounts again, and importantly setup a password which you can remember or use some password managers.