First you need to have Guan yu's escape for cao cao's force if you do not have this look at the parragraph

First you need to reach the 6 gate (which is the last gate) when you reach it there is a a note that there will be a supply captin. try to reach the captin and kill him (make sure Guan Yu reaches the 2nd gate when you try to reach the supply captin) when you kill the supply captin pick up the item and then kill Guan Yu if You fail you don't get the item.

How to get Guan Yu escape for Cao Cao:

If you want to get Guan yu's escape , in chapter 1 skip the yellow turban meance and the yellow turban fortress. then on chapter 2 complete si shui gate and Hua Loa Gate . Then finish Chapter 3 and then you get Guan Yu's Escape (in the the Yuans Family Pride you can either kill Liu Bie And Zhang fie or you can let guan yu go to them.)