Hmm I still can't seem to get that to work, here's my steps.
Start the game (DarkSoulsIII.exe, v 1.03)
Load my save file
Game is loaded
Sit at bon-fire
Alt-tab out
Start the trainer (Dark Souls 3 V1.03 Trainer +16 MrAntiFun.EXE, right-click -> start as administrator)
Go back to game
Press F1...