Adding Google event snippet to another page than the checkout page

Hi !

I am running a Google adwords campaign whose aim is to capture leads through an enquiry form : https://www.timbres-experts.com/pages/estimer-une-collection-de-timbres

I want to track conversions on the “thank you” page of this form : https://www.timbres-experts.com/pages/estimation-a-domicile

Google tells me that I need to add the “event snippet” in the header of the page, but I don’t know how to do that.

Can anybody help me ?

I don’t want to use the shopping cart function in this case. It is just for lead generation.

Thanks !

Vincent