see this post:
https://community.ccleaner.com/t/how-to-roll-back-from-v7-to-v6-39/156249
sorry that you had problems after running ccleaner 7. the older versions of ccleaner also have the potential to cause problems, like when using ccleaner to update drivers, for example. so, be aware of that. in other words, if you wanted to avoid possibly having problems, as a result of using ccleaner to update your computer’s drivers, then don’t do that.
personally, i have always experimented with things, understanding that there can be problems which could require doing a “clean” reinstall of windows. (sometimes, i’ve had to “clear the NVRAM,” too)