In our theme, we use only one sidebar for all page. You can use Widget Logic plugin to choose which widget you want to show on your page.
Go to Appearance >> Widgets and see the Sidebar widget there.
For example below, the Recent Posts widget only appears on the page that has ID 69 and all child pages of this page. “is_page” is one of conditional tags, you can choose others at conditional tags.
To search for the ID of the page, go to Dashboard >> Pages, then point at the page you want to take ID, its ID will be running at the bottom.