How can reset my iPhone passcode without losing the data?

If you KNOW your device’s passcode, you can CHANGE it without data loss.

If you DON’T know the passcode, a RESET will completely erase the device - returning it to a “just out of the box” state - and allow a recovery of data from backup.

The degree of data loss will be determined by how well (and how recently) the device was backed-up and sync’d.

How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

Note: If the iOS is prior to 15.2, reset instructions are linked near bottom of article in the section titled, “If you can't reset your device.”