Help potty training 😫

Jannia • Momma to a :4yr old 👧🏼 2yr old 🧒🏽 and 👶🏼 due 08/04!

So my boy will be 3 Sunday on the 9th and still is refusing to potty train it is frustrating because he knows when he has to go and where to go and when he has gone. He was almost fully potty trained a while back no peeing or pooping on long trips or while sleeping and telling me when he had to go but he spent a day with my mom and she didn’t follow my instructions and he completely regressed talk about one step forward and two steps back. Anyone have a similar problem or any ideas please help me, my oldest was so easy and I also have a 6 month old now help!!