Welcome back to the community. 
A trainer is not possible, as @XC3758 stated above.
The reason for this is that Diablo 3 is entirely server-sided (requires a constant internet connection to the game servers), even for solo play.
This means the game is running from a server hundreds of miles away from your PC, and there are no memory addresses being used by the game in your PC’s RAM for a trainer to inject its code into. Trainers are only for client-sided games that run entirely from your PC.
Anybody saying they have cheats for Diablo 3 is scamming you.