Is there a way to add a visit number to my electronic visit report?

Yes, when the author is editing the EVR, there is an "Add/Edit Header Note" button in the VISIT DETAILS section of the Report Header.

Clicking that button will display an area where comments can be entered. It is in this area that the author could enter text such as "Visit Number 2" to track the number of visits done at the site. When "Save" is clicked, the text now appears next to the Visit Note field in the header.