Altering MailChimp Integration ADD ON to comply with GDPR

The above Add On allows users to input their email address in a side box to be added on to MailChimp so the add on was written for just this one email field to be input. In Europe to comply with GDPR a tick box is not necessary for the use to tick to confirm they want to subscribe so an extra field is required.

In he documentation it states extra coding can to added to include an aditional fields but I haven't a clue how to do this. Has anyone achieved this which is necessary if you have any viewers in the EC.

Thank you.

Trevor