Adding Code to Button for Google Conversion Tracking

Hi, I'm trying to use a button on my Google Ads landing page to track conversions. I have the Google Tag and snippet installed correctly in the header, but I can't figure out if it's possible to edit the existing button's code (Book an Appointment!) on the page without adding a code block and having to format an entirely new button from scratch with html. 

Page in question: http://www.sukihairstudio.com/google

It just wants me to add the following to the body of the website, which as far as I can tell I don't have access to (I do have a business account). 

Thanks for any help!

You can add button with that code, then we can style it same as current Book Appointment button.

Can you copy code in your screenshot and paste here? We can adjust it easier

<button onclick="return gtag_report_conversion('http://example.com/your-link')">Submit</button>

Thanks!