In the Seoul map, there is only on sky bridge that you can actually walk through connecting two buildings, all you have to do is blow up one side with whatever you have explosive.
I found it easiest to use the red cylinders that you see standing around, pick them up with
and aim it at the steel reinforcements on the side wall at the opposite end of where your standing and shoot it with
. Do the same for the other side of that end and it should come down. If not just blow up the end you didn't.
Another easy way is to use the Light build, and have the breach charge gadget equipped. In match you can equip this by pressing
and the corresponding
, then you throw it by pressing
and blow it up by pressing
.
If you give a downvote, kindly let me know why so I can improve or if you need help let me know.(Video to come)