Please help accompany with the customer to perform the online inspection on 01 Sept. < It's not clear what you mean by "accompany with the customer". I can only tell you that it is incorrect.
What is the schedule for the 1,516 pcs of AR2345? Please provide us your mass production start date as this is required/needed for the online inspection. < You can use either "needed" or "required" here.
I would use "with" in the phrase "provide us" - "provide us with", but it's not absolutely necessary.
Student or Learner