How can I export mSecure to iCloud Keychain?
I'm not exactly sure what you mean here. If you are trying to use the iOS Password AutoFill feature, you simply follow the instructions in this help article: https://support.msecure.com/en/support/solutions/articles/36000085078-ios-password-autofill
If you are wanting to move your mSecure data to iCloud Keychain, which is a question I have never heard before, that is not possible. You could try checking both the "iCloud Passwords & Keychain" and "mSecure" options in the Password AutoFill options screen which may allow you to save the data mSecure auto-fills into iCloud Keychain.
More importantly, what is it you're trying to do here? If you simply need to have your mSecure data auto-filled into account login pages in Safari, turning on the iOS Password AutoFill feature for mSecure will fulfill your needs.