XF 1.5 Adsense within first forum post

[Bombardier]

Could you tell me where to put my adsense code to have it display in the first forum post.
Also as a result of my previous PP and Vb site being closed down I get an error message as follows

The requested page could not be found. I would like to place adsense code on that error msesage too.

 

[Paul B]

This guide should help: https://xenforo.com/community/resources/responsive-adsense.2084/

This set of guides will help you to identify specific templates: https://xenforo.com/community/resources/how-to.4390/