Hello and welcome to WeMod. 
Do you receive any error messages?
Please make sure you are using the correct trainer for your game, This trainer here is for the Origin version.
- If you have the Steam version of the game, you need this trainer: The Witcher 3 Cheats and Trainer for Steam
- If you have the Good Old Games (GOG) Game of the Year version, you need this trainer: The Witcher 3: Wild Hunt - GOTY Edition Cheats and Trainer for GOG
- If you have the regular non-game of the year GOG version, a trainer does not exist but you can vote for it here: https://www.wemod.com/cheats/the-witcher-3
- If you have an illegally pirated version of the game there’s nothing anyone can do but tell you to buy it properly. WeMod doesn’t support illegally acquired software.
If you are dragging the icon from your desktop into the WeMod app, that is not the game’s executable, but the game’s launcher. The executable can be found by right-clicking the desktop icon and clicking “Open File Location”.
If this didn’t help, please reply with more information. Such as the game version, where you got it from and specifically what happens/what you’re doing/what you see.