Pictory AI fetches visuals based on the keywords in your text. To change the visuals on a scene, please follow the below:
Open the project and select the scene to change the visual for.
Go to Visuals > Library.
Click on the visual you wish to use for the scene.
You will see the visual applied to the scene on the right of the screen
You also have the option to upload your own visuals, under My uploads. Just upload your visuals and select them to be applied to the scene.