How to link the email with mein O2

Not at all, as long as you have not registered for My o2 with your prepaid card.

Hello ​@paniddapiri ,

You can order a new confirmation-link in your Mein o2 account. Have you registered your number yet? If not, you will first need to order your new SIM card by contacting my colleagues via Hotline.

Kind regards,

Rebecca