I have created 2 GDPR Repermissioning templates in Mailchimp (similar text, slightly different layouts).

They come with a guide on how to edit them (change logo and ensure copy fits what you offer) and how to set up a group in Mailchimp which people can then opt themselves into using a change profile link in the email.

Price is just £20 (for both) and you can email me joolz@thevirtualmarketeer.co.uk if you’d like me to send them to you.