You may be able to load an earlier macOS using Recovery, the HD/SSD partition on the computer's boot drive. Briefly, you may be able to load the macOS that originally came with your Mac, or the closest software still available, whatever that is.
Booting while holding Shift + Option + Command + r (if your machine has macOS Sierra or later), or Option + Command + r (if your machine has an earlier release of OS X) should restore an earlier version. Refer to the Apple Support Document, How to reinstall macOS for more info.
I would also like to point to another discussion, How can I download an older version of OS X/macOS?, which goes into much more detail on what macOS reversions can be restored using Recovery and other Apple resources.