I've never found a way to fully restore a course to a prior state, unfortunately. But, we have had some success by exporting a course from our beta and/or test environments. If the significant changes happened more recently than the last beta or test refresh, that might be a good place to start.

If you haven't visited them before, the What is the Canvas beta environment? and What is the Canvas test environment? Canvas Guides will explain how to get there.

We've had some success exporting an entire course from the beta environment and then importing parts of the course into the production environment to support folks who inadvertently overwrote content, for example.

Keep in mind that student submissions stay connected to the course in which they were originally submitted. Be careful about deleting and remaking a course if it holds any student work.