How to change iOS password?
I'm forget my apple iOS password. How can change it?
iPhone 5s, iOS 12
If you mean you forgot the lock screen passcode, see: If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support
If it is your Apple ID/iCloud password that is forgotten, note that iCloud uses your Apple ID and password. If you only have one Apple ID, it would be the same ID and password as you used to log into this forum. If you have another and have forgotten the password, see the following: If you forgot your Apple ID password - Apple Support