Automate media player volume of 1 device to affect another

Hi,
First of all I’m new to HA so go easy on me.
I have a small problem, I have on my dashboard a card with all the TV’s (the default one) when I try to control the volume of the living room TV, it doesn’t work. The control is over the Android TV box connected to it, but the remote is set to control TV volume and due to the use of my parents I don’t want to change that one.
But I found out that the TV’s DLNA can control easily from HA the volume.
So I though to do an automation that when I press the volume up on that TV (on the default HA card) it will also press a volume up on the DLNA entity and same for volume down.
But how can I do that? what do I enter in the “When”?