There sure has been a lot of header-footer questions lately.

If you only want the header content to be only on the first page, remove it from the other headers of the section...but FIRST, change Link To Previous to false. The default is ON (True). So you will have to turn it off. Then remove the content from the header(s) you do not want it in. That includes OddEven, if you have that checked.

One of the biggest and confusing aspects of Word is trying to fix headers or footers, after the fact. It is worth the effort to try and understand them, because if you set them up properly in the first place, they work well.