You, as a volunteer are not expected to do anything to complete photo requests. If you can do it, that's nice, but you do not have to and there is no expectation that you do. You are not rewarded or penalised by BillionGraves for participating or not in photo requests.
If you are getting email notifications about photo requests, you can turn these off in the settings menu. The emails are sent automatically and while they sound personally addressed to you or like a plea from another user, they are not. They are system generated and you can just ignore them if you don't turn them off all together.
If you wanted to complete a request in a huge cemetery you would need to spend some time researching Cemetery records online or sometimes offline at local libraries or local history groups, but most importantly my first step is the administrators of the cemetery. The will 'usually' have the best records and should be able to provide directions to a grave using plot numbers.
What I don't recommend is just turning up at a cemetery and wandering around for hours hoping to find a grave that may not even exist.
Photo requests are a nice to have thing, but please don't feel compelled to complete them, especially at the risk of affecting your own health or personal safety.
If you need help with changing your settings etc, please let us know,