Hi, this instagram page has some short videos and pics of Stevie singing with Harry:
https://www.instagram.com/hsflaws/
They did his song 'Two Ghosts' and 'Landslide' in these clips.
And these youtube clips just posted:
https://www.youtube.com/watch?v=zF-iv-lmD7A
https://www.youtube.com/watch?v=HpjPg6mHfsE