Can anyone help with my Header and Footer Disappearance issue?

I’m trying to fine tune the header and footer, but they both disappear after I pressed insert code “after” the website. A banner added to the bottom, but when I tried to remove the banner (which I have no ways to do it), the header and footer disappeared too.

Please help on this. Thanks.

For free support, you can contact the author but if you’re willing to pay some money, I could help you.