back out (of something)
To withdraw from or renege on something, such as a given commitment, promise, plan, or situation. She was considered a strong contender to win the local election, but she backed out at the last minute and continued working as CEO of her company. John was so nervous that he decided to back out of the marriage on the morning of his wedding.
back someone or something out of something
and back someone or something outto guide or move someone or something backwards out of something or some place. Judy backed the car out of the garage. Please back out the car. Don backed Fred out of the garage.