First you have to go the second level from the top and you have to have both teams do it.
There's a barricade that's kind of broken to the right.
You then have to take cover and you have to then get shot and get downed on the barricade.
You get revived and your on the barricade.
The path you have to take is the right fence and then your teammates make a line and you walk over their heads and hop over the fence.
You're then able to freeroam around. Enjoy!