Hi @jemmaanderson,
Welcome to the Dyson Community!
If you’re asking about the current UK Trade In promotion, you can find all the details here - there’s an FAQ section at the bottom of the page.
After your order confirmation e-mail, you should then receive a second email with instructions on how to return your old Dyson machine, including how to get a pre-paid label and how drop off your old Dyson machine at a Post Office for it to be returned to us. If you didn’t get this email yet, please double check it hasn’t accidently been categorised as spam or routed into your junk mail folder.
To receive a £100 refund, you’ll need to return your old Dyson machine within 14 days of receiving your new Dyson vacuum.
Hope this helps!