How to switch a game in a multi-slot cabinet?

Today I've gone to an Arcade for the first time in a while and saw a MVS with 3 games: Puzzle Bobble, Neo turf Masters and Metal Slug 3. Nobody was playing so the three were rolling in circles one after another. The question is: if I want to play a game that is not the one in display, how can I do that besides waiting for it to appear? In theory there should be a switch button, but I couldn't see it anywhere. Any other way?

Was it a dedicated Neo cab or some kind of conversion ?
There must be a switch somewhere to change games.
Unless its a conversion and the joystick is wired up to do it.
btw the game select doesnt work untill coin up, it will just cycle from game to game.

I guess you have to insert a coin first, there is a button which allows you to select. At least it works on my 4 slots cab.

Well, definately it didn't look like a true MVS cab, more like a conversion. It had 5 buttons for each player, maybe the 5th one for (say) player 1 was the switch button. I didn't try pressing it in the "press start button" screen after I introduced a coin.

Thanks for your answer.

There should have been a switch button in the upper-middle, between both sticks.. That is where most cabs have it.