To create a video page manually, first identify the YouTube video id. Go to the video's page and copy the letters and number after the equal sign. Go to WordPress dashboard, click on "Add New" button, paste the id to the key field, set the video title and other fields. Click Publish.
If you see "Please enter a unique value error", it means there is a video with the same id already published or put in trash. If you have the same video already published, you do not need another one. If it's put in your trash, empty it by opening the trash list in another browser tab and then click publish again.