What technology are you working with @Foxglove ? Do you have a smartphone (or have acces to someone else's), and if so, is it an Android or an iPhone (or something else)? Do you have a computer or laptop with a built-in camera (usually just above the screen), or are there any at your local library you could use (if you're able to get there)? If so, is it a Mac/Apple, or a PC using Windows? Based on what tech you'll be using to shoot the video, I can help you find step-by-step instructions.
If you don't have access to any of the above (and maybe even if you do!)... the easiest thing would probably be to ask someone in your life who has a smartphone (especially a younger person) to help you out by taking a short video of you and emailing it to you. You could try asking a family member, neighbor, personal care assistant if you're lucky enough to have one, librarian, etc. If you're bedbound or housebound and the only people you can think of are far away, a last resort could be to ask them to make a video on your behalf, in which they can, say, hold up a picture of you ans say you don't have access to the right technology but still want to be seen and heard.