I was awarded full custody of my 3 children when they were removed from their fathers home because of drugs, domestic violence, neglect. The court granted him visitation but I want it to be supervised and I want him to take a drug test before each visit before I just let my kids go back to him for overnight visits, how do I do this

You don't get to make that decision yourself... only the court can order that. You would have to go back to court for that.

Did you ask for that at the custody hearing? When was the custody hearing? If it was recent and the court did not grant supervised visits, it may not entertain a modification at this time.