how do I connect the ccleaner app on my iphone to my professional ccleaner on my pc?
I’m not sure what you mean by “connect”?
If you are meaning that you have a multi-device and want to use that key on an iOS device then I’m afraid that is not possible at the moment due to Apple licencing restrictions.
You wiil need to purchase a second subscription/licence for CCleaner iOS through the Apple Store.
As a multi-device licence does cover MacOS we do expect that in future it will cover iOS too, but it doesn’t yet.
(It was similar with CCleaner Android - when that first came out you could only licence it through the Google store until an arrangement was reached).