Customer will not perform the online inspection, only Mr. Chan and some engineers from our company will arrive your factory for the online tomorrow.
One problem is that "only" has a couple of meanings.
What I think the sentence means is this:
Customer will not perform the online inspection,
> This is a complete sentence. It should end with a period.
> Use "The" in front of "customer"
- The customer will not perform the online inspection.
only Mr. Chan and some engineers from our company will arrive your factory for the online tomorrow.
> This is a different sentence, so it must begin with a capital letter
- Mr. Chan, along with some engineers from our company, will arrive at your factory tomorrow for the online inspection.
(NOTE: You can drop the word "inspection" if this inspection is often called "the online" by the people in the factory.)
The only problem is what you mean by "only Mr Chan ...."
If you mean that Mr. Chan only (and some engineers, but not the customer) will perform the inspection, then you don't need "only" and you should leave it out.