I don't know where my header is

There is no edit side header button that shows up. There were edits that were made to our website previously and I think the header was removed. How can we put it back?

Check Custom CSS (under Design) to see if the header is hidden, e.g. header {display:none;}. If it's only hidden on one page, check the specific page Settings (Pages) for any styles added to the header code. If it's not that, then check the Advanced Settings for Code Injection, where there may be a script or even a linked CSS style sheet controlling the header display.