The connection is actually reverse: A soundbar can be paired to the Apple TV box. Set your soundbar in Pairing Mode (see its manual), then discover it from Apple TV: Settings﹥Remotes and Devices﹥Bluetooth﹥Other Devices﹥…
Use Bluetooth accessories with your Apple TV - Apple Support
Subsequent use can be done faster after first pairing, through Control Center, and its Audio widget.
Quickly change settings in Control Center on Apple TV - Apple Support
Note that bluetooth connections are temporary in nature, and may start out disconnected for a next use.
Depending on your setup, pairing to Apple TV may not be needed, if you can connect it to your TV. Then the TV can passthrough any audio to the soundbar, regardless of whether the source signal originates from Apple TV, regular TV coax “antenna” input, or a different HDMI device.
Bluetooth is likely of lesser quality than a HDMI connection, if that is also supported in your setup. Bluetooth audio is recompressed stereo audio, while HDMI can be lossless multichannel (surround sound/Dolby Atmos).