Setting Space Between Thumbnails in your Product Gallery is very easy with the Woo Gallery Slider Pro plugin. Follow the steps below:

(1) From your WordPress Dashboard Menu, navigate to WooGallery Slider > General. 

(2) Under the General settings tab, you will find the Thumbnails Space option. Set the value of the Gap between the images and the Vertical Gap in pixels as per your need. 

(3) Click on Save Settings and refresh the product gallery to see the changes. 

The final output would be something like below: