How do I convert a Google Merchant test feed to a live feed

Google Merchant Test Feed vs Live Feed

You can’t.

To enable a live feed, you will need to create a new data feed using the standard mode (live).

What is the difference?

The mode designates whether or not your product data is eligible to appear in results.

Standard feeds create items eligible for Google Shopping results.

Test feeds do not create items available for Google Shopping results. Upload a test data feed in order to check and fix any processing errors and warnings before submitting the same file as a standard feed.