Auto grabbing thumbnail URL for cutom image field

Hey everyone. I’m not a coder so kindly bear with me on this silly question. I’m using a theme called WooTube which has custom fields for thumbnails and video embed codes. And I have a plugin that Auto grabs videos from tube sites based on keywords and creates posts regularly.

Both are working just fine but my problem is with the thumbnails. My plugin creates a thumbnail which it uses in the beginning of every post. How can I make my theme automatically grab this image for use in its custom field so the thumbnails show on the homepage?