Hi
Since the latest update of C Cleaner when I hit analyse the results come up with Thunderbird; Internet History, Internet Cache & Cookies "Skipped".
How do I sort this?
That sounds as if Thundebird is still running (maybe as a background task?).
CCleaner can't clean applications that are open/running so it skips them.
Task Manager should show you if it is running in the background, and you can force it to close from there.
You don't say what OS you have, if it's Windows 10 try taking a look at:
Settings > Privacy > Background apps