Add custom code to submit button on the sign up form

I want to use Google Ads conversions in order to track conversions, but I need to add a function on click to the button. As I can find no option to the edit the code of the button I’m unable to do this. Please help me with it

If you are doing it through your own custom code, then you should just add it to the button’s onClick call in your code.
https://www.wix.com/corvid/reference/$w.Button.html#onClick

If you aren’t using code for your site, then you are best going through Wix Support for more help as this forum is only for code users.
https://support.wix.com/en/article/adding-a-conversion-tracking-tag-to-your-wix-site