If you can't find a suitable picture in Unsplash library, you can always upload it from your computer. Since you are in the Editor, click Change button.
You will see pictures you used in other projects. To upload one from your computer, click Upload Media.
Select the image you need and click Open.
Your picture will appear in library.
If you have a lot of pictures from other projects and want to sort it, click This project to see pictures from your last project only.
To add a picture to your project, check this box first.
Finally, click Place image.
It's done! Your image will appear in your project.