How to add mail variable to newsletter block to auto-fill in mailchimp?

Site URL: https://point-plane-h5zc.squarespace.com/contact

How do I add code so to this mailchimp email field is autofill after a user entered their email and clicking the sign up button in the newsletter block?

Mailchimp link:  https://whiteribbon.us9.list-manage.com/subscribe/post?u=85ede3cf5ce145c9558837595&id=7fcf20cbc1

I need it to work where after a user has entered their email and clicked sign up, the mail field in the mailchimp link page has been autofilled with the email they have put in the email field in the newsletter block.