Is it possible to restore the Knowledge Base back to base system values?


It is not possible to revert a particular application (in this case, Knowledge Management) to base system values


There are certain ways that we can try to reset an application to OOB as mentioned in this community article: Can Knowledge be reset back to OOB?

The method specified in that community article is not supported but it is a widely used technique.

If you choose to apply the same steps, please test this in your sub-prod instance and make sure it doesn't cause any issue before trying it in the production instance.