Best way to do it is kill the 6 thrall, step back off the plate and aim at the sword beater coming down the stairs with a sniper. Hopefully he is running right at you and not to the left or right. Hit him in the head to stagger him and get him to come to you and move back onto the plate. The bridge should form as you kill him or just after u kill him and get the sword. You can move of then back on right away to avoid his swings if need be. When it forms run up the light bridge part jump and swipe your way across. If you go before the message says it has formed you don't get enough height and you fall short and down I to the pit. Also helps if you can one shot the 6 thrall so I get a clear view of the swordbearer.

You have to keep hopping on and off, so it doesn't wipe you. If when the message shows up on your bottom left corner, you get off the plate immediately, then back on when it disappears, you can raise the bridge solo.