My 3-year-old child has been enjoying his preschool. However, recently he cried not to go to preschool, how do I persuade him to go?

It could be something happened in the school and cause him to behave in this way. You should check with his teachers in school if there is anything happened in school e.g. bullied by friend, misbehave and punished, fell down and etc. 3 years old I guess is still too young to tell the whole story and thus try to communicate with teachers and understand what is going on and help your kid from there. My daughter, when she was in N1, refused to go to school and I found out from teacher that the teacher scolded another student who was misbehaved in class. Thus, I explained to my daughter teacher was not scolding her and will not scold students who are behaving well. After that she is not so traumatised by the event and love going to school again.