How to Setup & Redirect Customers to a Default Custom Thank You Page
This option can be useful when a cart contains multiple products with each product having a different thank you page URL.
If there is no URL defined at the product level, then the customers will be redirected to the default thank you page URL.
Follow these steps to redirect your customers to a default WooCommerce custom thank you page after checkout. This is for users having WooCommerce version 3.4.0 and above.
Step 1: Go to WooCommerce > Settings > Advanced tab > Page setup.
Step 2: Find the ‘Default Thank You Page URL’ field.
Step 3: Enter the Default Thank You Page URL and then click on Save changes.
If you want to set up a custom thank you page per product, please refer this doc.