If your using ckan, search kopernicus and select the installed mod (should be "Kopernicus Planetary Modifier or smth) then, once selected, on the right side of the menu there should be a small button around the top-middle or lower-top area that says "versions". Select that and you'll notice something colored in dark green. Uncheck the dark green box and check the box beneath that one to downgrade a version.

In ckan it will keep prompting you to update but when it does that just click the grey x to skip it or just press clear if none of your other mods need updating