I installed Skype from the website a couple of weeks ago. As I was refreshing the Synaptic manager, so I can do an update I got an error message that the signature couldn't be verified.

Here the error message:
W: GPG error: https://repo.skype.com/deb stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1F3045A5DF7587C3
W: The repository 'https://repo.skype.com/deb stable In Release' is not signed.

Any idea how can I verify, and download the signature, and update?

I found the answer, and resolved the issue here.
https://repo.skype.com/