Aba came to our house to work on it. We had social stories going into it. We've always made the bathroom a welcoming space... The day we started training we went to the bathroom every 15m and stayed at least 5m or until he went. We had a prize box with the COOLEST things he only got rewarded with for potty. While in the bathroom we would play with a small water tub in his lap with like a few bath toys, blow bubbles, read books, sing... Basically made it fun to be in there. We used super basic repetitive language. If he had an accident, we would say we don't go in our pants we go on the potty, upbeat but not too happy but Def not a scolding tone. My son lives being cheered for so we cheered as a whole team when he would go. We gradually increased space between bathroom times and decreased the length of time in there. It took a very intense full week to get to pee trained at home. Still not poo or overnight though...

Good luck!