New domain and email set up. Using 3rd party domain host and Squarespace

I have a website set up on squarespace. I need someone expert at using this platform
My domain and email is set up with another provider
I have obtained a new domain name
I wish my new domain to be used on squarespace and the enquiry function on my website to be the new email
I need this all tested and converted please
I will obviously provide passwords etc to the contractor