Signia hearing aids and Apple TV 4k

if they use the usual bluetooth profile called a2dp which most headsets and Bluetooth speakers also use

then you pair it like any other speaker

Use Bluetooth accessories with your Apple TV - Apple Support

mind you you need to make sure the "headset/aids" does not have an active connection with your iphone or other devices when you pair it with the appletv

and of cause the aids need to be put into pairing / discovery mode the first time, how you go about doing so should be on the manufactorers site and or documentation

If these support regular Bluetooth, then they should be compatible.

Use Bluetooth accessories with your Apple TV - Apple Support

Initially (one time action):

1. Set the bluetooth device in Pairing mode (see its manual),
2. Navigate to Settings﹥Remotes and Devices﹥Bluetooth﹥ on Apple TV,
3. Locate the detected nearby Bluetooth device in the list under ᴏᴛʜᴇʀ ᴅᴇᴠɪᴄᴇs,
4. Select that device to pair and connect. A pairing code may be required.

Next time, the pairing will be remembered, and you only have to connect from your list of bluetooth devices.

Either in the Bluetooth screen, or in the headphones/audio controls in Control Center.