Navigate to your storefront. Mine is https://www.amazon.com/shop/entreresource

Upload your video file. The dimensions can vary without issues. It might take a minute or two to upload. 

Give your review a catchy title.
Click submit post.

Click the tag products option to find the product you've reviewed. 

Click the "Search Amazon" field.
Type the name of your product and find it in the search results. 
Click "elgato stream deck"

Type the name of your product and find it in the search results. 

Select the check mark and click done to complete.
Click "Done"

Select the check mark and click done to complete.

If you'd like to add a unique thumbnail (recommended) click the add thumbnail button and select your image. This will be what Amazon shoppers see. 

You will receive a video submitted notificaiton. Your review will be live within about 5 hours. 

amazon.com

How to add a video review to your Amazon Influencer Storefront. You will need to be approved for the Amazon influencer program for this to work. 

Amazon Influencer Program Video Review Upload Tutorial