Electronic – arduino – Pressing a physical button, but digitally using an Arduino in an existing circuit

I have a pair of speakers that by default select their input as bluetooth and I have to press a physical button (every time I power them up) to switch their input to auxiliary.

So I'm thinking of a small arduino based project where every time the arduino starts up (I will wire it to get 5V when the speakers start) it will simulate a button press.
The software part is easy, when the arduino starts, just output the correct voltage on one of the pins, connected to the switch.

Trouble is that I need to press the switch just once (if I press it more than once, the inputs will cycle) and I cannot really understand the electrical schematic.

So as you can see there are 5 switches, all connected to the pin 45 of the MCU.
I want to simulate a single press of the SW10/INPUT button.

Conceptually I think the pin 45 measures the voltage (since every button is series with a different resistor) in order to find out which button was pressed.
So, is the AD_KEY line connected to the MCU between pin 45 and the 3,3K resistor?
Just like a voltage divider?

If yes, does this mean that on startup, and only on startup, it is sufficient to output 1.2V [a] from the arduino to the AD_KEY line (which leads to pin 45, where the speaker's MCU will read) in order to simulate a button press?

Electronically, is there a way I can do this just once at the beginning, without wasting an mcu/arduino (even if just a micro arduino) here?

[a]: If we're talking about a voltage divider then when SW109/INPUT is pressed we have:
$$
V_{pin45} = V_{in}\frac{R80}{R80 + R1} =>
$$
$$
V_{pin45} = 3.3V\frac{2K\Omega}{2K\Omega + 3.3K\Omega} = 1.24V
$$