@Christine, multiple sidebars feature by default is not available in theme. However, you can add them by making a new Child Theme and write some custom codes.
So overall approach would be
1. Make a Child Theme and activate
2. Write code to register new sidebars
3. Edit page.php and add code to make compatible for multiple sidebar
4. Add widgets to given sidebar and make them able to choose and display from specific page.
If you need any customization help, consider Hiring a Customizer to make your theme programmed with this feature.
Thank you