Please my girlfriend just locked her iphone 7plus. And it says we should connect to iTunes. Please we need assistance on how to retrieve the passcode please

There is no way to retrieve the passcode. The passcode only lives encrypted in the iPhone and in the mind of whoever set it.

If its been disabled and requesting you connect to iTunes, then that is the only option you have. Follow the steps here: If you forgot the passcode on your iPad, or your iPad is disabled - Apple Support

You will need to restore the iPhone and set it up again. If there is a backup in iCloud or iTunes it can be used to restore the iPhone so as to not lose data.

See If you see a message 'Your account has been disabled in the App Store and iTunes' https://support.apple.com/en-us/HT208856. This link says: "There might be a problem with the payment method that you have on file. When you see the message, don't try to edit any of your account information. Instead, contact Apple Support for help.”

Try using the Apple recommended support link above first. But, this site is down/not fully functional very often. Use the support options I give below if necessary.

You can use Apple Support Twitter https://twitter.com/AppleSupport  There may be a wait of an hour or so.

And, if necessary, go here to contact iTunes worldwide support via text or chat https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading, Tell us how we can help.