How do I unlock my iPhone if I forgot my passcode?

If you have forgotten your iPhones passcode there is no other option but to erase your device. I hope that you have a backup

1. From your device's Lock Screen, try to enter your passcode until the "[Device] Unavailable" screen appears and your device asks you to try again later.
2. When you're able to, tap the Forgot Passcode? option in the bottom corner of the screen.
3. On the Security Lockout screen, tap Start [Device] Reset to confirm.
4. Enter your Apple ID password to sign out of your Apple ID on your device.
5. Tap Erase [Device] to permanently delete all of your data and settings. If you use an eSIM with iOS 17 or later, you can also choose to keep your eSIM and erase your data, or to delete your eSIM and erase your data.

6. When your device restart, follow the onscreen instructions to set up your device again, restore your data and setting from a backup, and set a new passcode.

If you can't follow these steps, you can use a computer to reset your device.

Your data is not lost if you have a backup either on iCloud or iTunes.

If you see an iPhone or iPad unavailable message or a "Security Lockout" screen

If you forgot your passcode, you can use your Apple ID and password to erase and reset your device without a computer.

Learn what to do if you see "[Device] unavailable" or "Security Lockout" on your iPhone or iPad.)

iPhone is disabled.

Following this process is the only way out if your iPhone is disabled. The steps given in this link will help you reset the passcode -> If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ...

Regarding your data…

1. If you have an iCloud or iTunes latest backup, then there is nothing to worry about. If not read more...
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; the information that is 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 have turned on iCloud Photos, your content is automatically stored in iCloud.)
3. You have imported your Photos and videos to Mac/PC then they are safely residing there on Mac/PC
4. You have uploaded some of it to Cloud Drives using the Files app (iCloud Drive, Google Drive, OneDrive, DropBox, Flickr, box, AmazonDrive, Adobe Creative Cloud, etc). The data remains there.
5. If you have not backed up or do not have the latest backup, nor imported nor you have synced or uploaded your data to cloud drives prior to the situation that you are in, then I am sorry, all your data is lost.

If you forgot a passcode that you changed within the last 72 hours, see the "If you recently changed passcodes, use your old passcode to temporarily sign in" section of: If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

Otherwise, see the other sections of that article

If neither of the above is an option, you will need to use a computer. See: If you forgot your iPhone passcode, use your Mac or PC to reset it - Apple Support