Creating a variable from an input field

I have a landing page on which a user inputs their email address.

They click submit and it takes them through to another page which has a few more more fields that the user can fill out if they so wish.

I’d like one of the fields to be their email address but be pre-populated from what they put in on the first page.

Any advice on how to go about this?

I’m using CF7 for the forms and have been looking in to using either a php variable or a url parameter.

I can’t figure out how i would make the landing page email input in to a variable though.

Help appreciated!