Step 1: go to steam support
Step 2 go to tf2
3 : problem with items
4 : go down and press contact stwam support
5: type down what acievement item you lost
Tip: make it desperate
Ex
I deleted my gibus because i have limited space
I deleted ot because people laughed at me and called me a noob

how can you get yours back? i deleted mine a long time ago because i didnt have backpack space