I have a gen 1 Apple TV but it doesn’t mirror on my tv, it just keeps Ali on my phone

Can Apple TV be repaired …

From what you’re describing, I’m not convinced anything is broken that needs repairing.

1. Not all content can be mirrored. Some content providers may not make their content AirPlay compatible. Some content providers may block AirPlay Screen Mirroring.
2. Both devices have to connect to the same home network. For Wi-Fi, that means the same SSID network name.
3. For Apple TV, the setting for AirPlay receiving has to be turned on.

Use AirPlay to stream video or mirror the screen of your iPhone or iPad - Apple Support

If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support

… or traded in for new one

“Trade In” is a buy-back procedure from which Apple TV boxes are excluded.

If you have warranty or AppleCare+ for this product, and anything is broken, then see here: Apple TV Repair & Service - Apple Support.

As previously stated it could mean the content in question is unable to be mirrored, the other possibility is that there is a network issue (if you are trying to mirror then that requires a stable connection in order to send out your display in real time). You could try with various content and also verify the connection (try wiring ATV instead, use diagnostic tool on computer like istumbler to see signal/noise/nearby networks).

You could also take it in to Apple so they can test, but if the problem is related to the above then it is unlikely they would find an issue.