scout ball

So, as N. Corp Inquisitor. stated, using the scout character, you press "B" to throw a scout ball. Go up through the small vent, get to the button, align yourself as well as possible and press "E" to activate it.

Since you didn't know about the scout ball, I'm gonna assume that you also don't know about the steel cutter. The engineer has one that is used to open a hole. I don't remember the key but you can either find it in the keybinds menu or open your inventory (with I) and click it.

Finally, I'm also gonna assume that you don't know about the rope that you can put with your scout (which is different than the grapling hook). This one is accessed with "." and lets you help your engineer friend go through holes and stuff.

In general, just open up your inventory and experiment with every button so you know what they do. Also a quick read of the keybinds could help as well.