The transfer time of primary schools in Tianjin is one week before and after the start of each semester. No transfer in sixth grade. Now it's all student status, and transfer is also student status following others, so you can't repeat the grade. Unless you quit school. Of course, I suggest you call Binhai Education Bureau.
Conditions for transferring to Binhai New Area:
① Students are not allowed to transfer at will during school. If the registered students in Binhai New Area really need to transfer due to the change of their registered residence and legal fixed residence, their parents or other legal guardians shall submit a written application to the transferred school.
② The accompanying children of Tianjin residence permit holders shall go to the schools affiliated to the school district for transfer registration one year in advance in accordance with the Measures for Registration of Children of Tianjin Residence Permit Holders in Binhai New Area.