Need help with potty training

Martina

My son is 3 years old he still won’t go to the toilet I’ve tryed everything possible but when he goes in his diaper he’ll go in his diaper & he gets it all over why dose he go in his diaper & gets sh**t all over lol 😂 why his he doing this He used to tell me to change his diaper he dose that instead & it so nasty & don’t what to do!!!!