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Piling into the bus is an excellent idea. Perhaps if there were 30 team members it might work. Unfortunately with only 6 of you, there is not enough weight. However, you are on the right track in a way.

Ok. Then shoot or use axe on the tires. That way, the bus will be lowered , thus the button will be pushed

Rather a drastic measure when you could simply unscrew the tire valve and release the air pressure that way, but yea.. the gun works, but you don't have one. So... you lose all your actions chopping away at the tires to lower the bus onto the button. The button makes a 'click' sound.

I did think about that. But after finding the valve, there is always a round hole with a pin in the center. That pin should be pushed at a certain pressure. I can't find the certain amount of pressure inside the tyre and also I don't have any thing to push the pin.
That's why I thought to put holes in the tyres.

I just use my fingernail to depress the valve mechanism, but fair enough. You accomplished the goal. It matters not HOW; just that it was done.

I'm working on today's update as we speak.

So, what happened after the click sound ? Are we going to find out in the next day ?

The click closes an electrical circuit. You now have power. If this was done later in the game, it would have been much more difficult to figure out the solution. It should be quite easy now.