Your Cover Photo is the first thing people see when they visit your profile page, it should be as creative and eye-catching as possible.
Here’s a good resource to make a cover and matching profile picture
Or you can make your own cover if you have fantastic photos and remember that the dimensions for a Facebook cover photo are 851 pixels wide / 315 pixels high
You could also use one of the photos available for download from Unsplash. These photos are free for use.