How to make little one sit properly and eat during meal time,

My daughter is 19 months old now. Before she sit on her chair and eat well when during the meal time, but recent weeks starting to refuse to sit on her chair, and run, play around during meal time, my helper has to feed her and she play at the same time. I know is bad. I want to fix it, any mommy has good advice on it? (Is it the time she supposed to eat herself without people feeding her?)