I think this is not quite the correct forum for the question. Probably you will also be able to easily google an answer.
One option:
If you have access to Adobe Photoshop, just create a new file in your desired aspect ratio.
A typical resolution with a video aspect ratio (Full HD 16:9) would be for example 1920x1080 pixels.
Then you open your photo and copy the photo layer into your new file. Just position the photo and save it. It will then have a 16:9 format, like a Full HD video.