This button only appears in the YITH Gift Cards settings when the WooCommerce Smart Coupons plugins is enabled.
With this feature, you can import “Store Credit / Gift Certificate” Smart Coupons and turn them into YITH Gift Cards in a few seconds. Just click on the “Transform” button. The customer will than be able to use his smart coupons as gift cards in the shop.
It is very important to disable the WooCommerce Smart Coupons plugin, after the transformation or at least delete the transformed coupons. If you do not disable/delete, customers will be able to use both.