change where a button links to

I have a page that I changed from a post to a page. My main theme has a button on it that used to point to it when it was a post but now it is a page and does not point to it. This is a custom theme built by a man I am no longer in business with. How to I change where the button links to? It now points to a post called blog that I no longer want it to point to. I just need to change what this button links to. I’ve Googled this for hours and found nothing. Please Help.