I had a popup asking if I wanted CCleaner to stop a program OLB from making changes - I accidently clicked yes so now when I run OLB it comes up with endless error messages that it can't change various files. How do I undo this?
CCleaner does not do that. CCleaner is a junk cleaner, with a few other maintenance tools.
It's more likely your antivirus/antimalware that is blocking a programme from making changes.
CCleaner is not an antivirus and can't block other programmes.
Having noted that:
OLB most commonly stands for 'Online Bible' - Why a Bible would be trying to change files could be a worry.
There are a couple of backup apps that include a file named OLBPre.exe which is commonly linked to Adware, so your AV may have seen that.
Check your Antivirus logs and 'un-quarantine'/whitelist the app if you still want to risk it.
Otherwise uninstall that backup app and choose a more reliable one.