Start small
Sit is easiest to learn when the dog can choose the movement instead of being physically placed.
There is no need to rush. A predictable, manageable step is usually more useful than trying to solve the whole situation in one day.
Try this next
Lift a reward slowly from your dog’s nose toward the top of their head and reward when the back end touches down.
Notice what helps your dog stay comfortable and engaged, then repeat that version before making the situation harder.
Keep it kind and practical
Keep the next step easy enough that your dog can succeed. If you are worried about safety or feel stuck, pause and ask a qualified reward-based professional for help.