I have Acorn TV on my computer, how do I transfer Acorn from my computer to my Sony TV? I just added Apple TV HD, model MR912CL/A to my sony.

Download the Acorn App from the App Store on the Apple TV box, and sign in with your Acorn account.

If you are using the Acorn Apple TV channel in the Apple TV App on your iMac, then it should automatically have been activated inside the TV app on the Apple TV.

You may need to update the Apple TV box to the current software version to get the newer TV App with the internal channels.

See here: How to update your Apple TV - Apple Support

I do not know anything about Acorn TV, but if it functions as Apple TV does, you don't "transfer" it. You "add" it to the TV. I think you have to go to the TV and use its interface and commands to activate it in the smart TV. I recommend that you consult your Sony TV manual for details, or possibly their web site. The information you need is on one or both of them. The problem is that every new smart TV is different and has its own interface. Good luck with it.