First, logon Shopify admin backend and then go App section

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/c73d2118-c142-4d75-a21d-c5a51b3cc7a9/Screenshot_2021-01-15_at_11.47.52_PM.png

Look for the Connected Inventory and click Delete.

Finished.

If you have uninstalled before the trial end, you won't be charged.