Click the folder icon of the Target Application section and select Browse. You have to navigate to the folder you have installed Legend and choose the trl.exe file. It is most likely somewhere in C:\ Program Files\ Crystal Dynamics\ Tomb Raider Legend folder, unless you installed the game elsewhere.
Switch to Package Mode.
Click the folder icon and navigate to the mod’s file. Choose the Amanda blue.tpf
The outfit appears in the box on the left. If you select it, you will get additional information on the right.
Hit Run to run Legend. Select the Amanda Outfit in game to use it.