I have Apple TV model A1427 (3rd generation). I can now no longer view ESPN. What do I do?

It's pretty close to being that easy. And, if you have a 3rd gen, it's probably quite a while since you had to do the set up so not surprising the details aren't fresh in your mind!

See here:

Set up your Apple TV - Apple Support

The interface is different (it's been a while since my 2nd gen so I don't remember exactly what things looked like) but not hard. You may be surprised at first at how few icons there are. That's because you have to download the apps you want.

Start here:

Download apps on your Apple TV - Apple Support

And, people are always here to answer questions.

Best of luck.

Unfortunately, a lot of the providers have removed their support for channels on the older Apple TVs. Both of the current models support the App Store and will allow you to download the ESPN app.