Hi, welcome to Just Answer. My name is ***** ***** I look forward to helping you!
Please know that I am not compensated for my time by the site until you rate using the stars at the top of your page. A rating is appreciated once we get to the solution for your appliance issue, thanks!
The frost is preventing the fan from running. It will need to be thawed to replace the likely faulty heater, number 32 in the diagram at the link below. You will need to unplug it and leave the doors open for a couple days to totally thaw and then the freezer floor will need to come totally out. This will require a great deal of disassembly!
The link below is to the part you will need from a highly recommended company rated A+ with the Better Business Bureau. They offer a 100% money back guarantee, EVEN ON INSTALLED ELECTRICAL PARTS, for an entire year! They are the only company to allow returns on installed parts for a refund and offer a FULL ONE YEAR WARRANTY!
Both doors do need to come off, followed by the metal trim in between the sections. Once they are removed the floor will slide out and the rest of the components accessed, see link below.
Please let me know if you have additional questions or need clarification. There is no additional charge for any follow up help!
Please remember to rate before you leave, using the stars at the top of the page. If you have any other questions, please let me know! You may continue asking follow-up questions until you have all the information you need, even after rating my service. Thank you!