First Copy the Showcase id from Product Showcase :
1-> Click on the Showcase from the left sidebar
2-> Then copy the Showcase id
After that add a showcase in section or block on the Page
1-> Select a page
2-> Add a block or section
3-> Click on Apps
4-> Select Product Showcase
Then paste the Showcase id of theme block or theme section :
1-> Paste Showcase id theme block or theme section
2-> Finally click on the Save button
