You’ll usually be able to change tax class at a Post Office, but in some cases you may need to apply by post.
As far as i know you cannot just transfer it over to another car you need the certificate of exemption.
I contacted hmrc for mein on 13th of june and it’s still not arrived they said 7 to 10 working days. Dealer taxed the car for a year as it was a new car but either way you cannot have a car on the road without tax. So If you don’t have the certificate of exemption you’llhave to tax it till you do then they will refund you for every whole month.