Firstly, make sure you know what email you used when you checked out as a guest. You should be able to find this out by looking in your inbox and checking the email address that DAYMADE's emails are addressed to (in the 'to:' part of the sender details).
Once you know what email you checked out with, you should be able to finish setting up your DAYMADE account by entering that same email address on the Registration page and finishing the registration: https://www.daymade.co.uk/register