What sit can I go on to add my first name to my own birth certificate the space for my first name is blank and I want to put my name on my own birth certificate

What country?
In the US, you have to be 18 to make changes. I'm not familiar with the first name left blank, so go to the county courthouse and apply (call first to find out where). You will have to stand before a judge for a minute or two, and pay a fee.

Are you sure that you have a registered birth certificate? You may be looking at one that wasn't complete.