Go to the Shopify Admin > Settings > Shipping and delivery and open the relevant Shipping profile.
Add a Shipping zone to this profile.
Add a Shipping Rate to this zone.
Add a Condition and select Based on order price. Enter a minimum order price that is the same value as the free shipping threshold in the app. In this example, $25 orders get free shipping.
When you're finished, click Done.
More details here from Shopify on setting up free shipping rates.