Hi and welcome on the forum.
Most likely your BV7 is a MK3 version.
You can find the User Guides etc to the BV7
link
As you see, you must register the HDMI port, you want to use for the ATV to an AV input and thereby choose which ‘button’ on the Beo4 remote, you want to use to activate that port.
The two HDMI port with cables are for the build-in DVD player and for the digital tuner (do not use these) - use one of the free ones.
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if you want to use the AppleTV (which version?), you must connect it via a HDMI cable as described above/in the Guide.
You must log in to the box with your AppleID in order to get other/additional apps etc there……if it is a newer version.
Or you can simply Airplay to it.
The ATV
must however, be connected to your home network (same as your iDevices) either with a network cable or via the wireless function, that you can configure in the menu of the ATV.
In order to control it, you willhave to use the small remote, that came with the ATV.
If you have further questions - after studying the Guide and having tried things out - feel free to get back with further questions.
MM