Header and Footer gone due to

Hey Guys,

I wanted to hide my header and footer on a landing page and did a mistake.

Unfortunately  I used the code in my actual footer to hide it and therefore on all sites both my header and footer dissappeared.

Since they are not displayed anymore I can not reverse my mistake, because I can not click on the coding window.

I already tried deleting the latest landing page, but since I changed the code in the footer the problem remains.

Do you guys maybe have any solutions for this issue?

I would really appreciate it.

CODE:
<style>.header, #footer-sections {display:none!important;}</style>

Kind regards,
Nico

I am trying it tommorrow.
Thank you very much in advance!