How can I get my screen passcode

What do you mean you didn't get any passcode? If you set up the iPhone you created a passcode. Have you forgotten it?

If you have use the directions in this link to erase your phone using your home computer and iTunes --> If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

Follow this Link

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled

https://support.apple.com/en-us/HT204306