The trick is to set your answer in a positive and constructive manner. Although your experience may not have been perfect, you can provide a valid excuse to quit a job, like pursuing a career, wishing to work in a more demanding setting, or seeking a more consistent fit with the goals of your career.
Concentrate on what you acquired at your last job and how it inspired you to proceed. Whine with no complaining or criticism and make it seem that your choice was considered and meant to gain personal and professional development.
Get more ideas here:
https://managetrix.com/resources/good-reason-for-leaving-a-job/ 
