Def take a class. You might be able to encourage your employer to have one at work.

Until then check if they're breathing and if not just do chest compressions, no mouth to mouth. Rotate with others as it's hard to keep up. Fast and hard as long as possible. You're circulating their blood for them.

For any situation where you're waiting for help someone needs to take control and direct people.

Give clear and specific direction to people.

"You (point at person) call 911,"

"You (point at different person) go to the front doors and bring the paramedics here"

"You (point at different person) clear the area so there's room for the paramedics"

"You find an automatic defibrillator"

AEDs are straightforward to use, but watch a video for how to so you're already prepared.