Easy. Inside your Player Controller blueprint, create/spawn the widget object that contains the animation you want to play, and then do the usual stuff to add it to the viewport. You should promote your widget object to a variable so you can access it when your key is pressed.
Also inside your Player Controller blueprint, set up your key press event. During that event, execute a Play Animation node on your widget variable. You can specify which animation you want to play, adjust playback speed, etc.