You'll have to clarify what you want. You want to track in Google Ads when someone fills in your contact page?
Create a Google Analytics goal based on the destination URL. Submit the contact form page yourself and copy the URL portion (after the domain) into the final destination. Import the goal in Google Ads from within the conversion section.
Run Google Shopping ads? Get the free definitive guide to Google Shopping for Shopify (no optin required): https://www.digitaldarts.com.au/google-shopping