Resetting iPhone screen time passcode

If you have forgotten your Screen Time passcode

Use this link to reset your passcode If you forgot your Screen Time passcode - Apple Support

If you are unable to reset Screen Time passcode from the this-> link then, you will need a computer. If you don't have one, borrow from a friend.

Forgot? Click below to reset…

Click->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ...

Regarding your data, If…

1. You have an iCloud or iTunes backup, I am sorry there is no use of a backup because if you restore from your backup your Screen Time Passcode will be back. 
2. You have synced your data to iCloud, then what you will get back is what you have synced to iCloud and uploaded to iCloud Drive; like the information that are synced and stored in iCloud are, Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, shared photos, iCloud Photos*, Health data, call history, and files you store in iCloud Drive. (*-If you had turned on iCloud Photos, your content is automatically stored in iCloud.)
3. You have not imported nor you have synced nor uploaded your data to cloud drives prior to forgetting the Screen Time passcode then I am sorry, all your data is lost.

Connect iPhone to Computer / Mac

Settings > Touch/Face ID & Passcode > USB Accessories > [Enable]

You haven't mentioned whether you have a PC or Mac. However...

1. Use your USB lightening cable --> Resolve USB-related alerts in iTunes - Apple Support
2. If unable to connect --> If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support
3. If your computer is a...
   1. Mac --> If your computer doesn't recognize your iPhone, iPad, or iPod ...
   2. Windows PC —> Troubleshooting issues with iTunes for Windows - Apple Community
4. Use genuine cable --> Identify counterfeit or uncertified Lightning connector accessories ...
5. See how to --> Sync your iPhone, iPad, or iPod using iTunes on your computer ...

If you are experiencing an issue not listed here, contact support