Any advice as to where I add GTM Javascript code?

Hi!

I'm trying to add GTM to a specific page to track performance. Google tried to help me install the tag, but said an ad blocker was preventing us from do so. I'm not what t hat means and I can't seem to find an answer (and Google isn't helping).

So, they told me to add the following Javascript to the page:

 

event: "contactFormSubmitted"
formid: 63
gtm.uniqueEventId: 14
inputs: Array(5)
0: {name: 'your-name', value: 'test'}
1: {name: 'your-email', value: 'test@google.com'}
2: {name: 'your-phone', value: '98765432345'}
3: {name: 'your-subject', value: 'test'}
4: {name: 'your-message', value: 'test'}

I put it in the Header Tag, and Google told me it wasn't firing (wasn't working). But, if I add it to the page directly, no matter which code block I use, it shows on the front end.

Any advice on this or GTM with SS?