Hi Pip (@pvalleley3585)
Sorry for the misinformation. Yes, you want to insert an HTML Extension and paste the embed information copied from step 3 as described in this article: https://docs.microsoft.com/en-us/stream/portal-embed-video
You can click the Edit button in the properties ribbon of the HTML Extension, then paste the embed information (see attached picture).
You will need to set the size of the HTML Extension on the position & size tab so it matches the size of the video.
Click page preview after doing this and the video should display.