Adding custom fields to Google Ads Conversion Tag in GTM

A client gave me a conversion event code using gtag / global site tag...

gtag('event', 'conversion',  { 'send_to': 'AW-XXXXXXXX/XXXXXXXX',      'customField1': 'submitted',      'customField2': 'something',  }); 

...which I am trying to implement via Google Tag Manager. However, I don't see a way to add custom fields (customField1, customField2) via the Google Conversion tag in GTM.

Am I missing something? Or using the wrong tag?

Thanks in advance.