Hi, My child forgot his password for his Apple ID. How do I reset the password. I am the organizer, but it doesn't allow me to change it.

My child forgot his password for his Apple ID

You state this is a child. If you set up the account as part of setting up accounts for younger children through Family Sharing this special method may be available to you:

Family Sharing and Apple ID for your child - https://support.apple.com/HT201084

- "Your email address is the rescue email address for your child’s account, and you can use it with the security questions you provided to reset a forgotten password. You can keep your your child's account more secure with two-factor authentication."

If this is an older child you can go the more usual route for a forgotten password:

Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487

or go directly to this link --> http://iforgot.apple.com/

Also read about "What to do after [or before] you change your Apple ID email address or password" - https://support.apple.com/HT204071

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." --> https://support.apple.com/HT204169

If you didn't receive your verification or reset email - Apple Support - https://support.apple.com/HT201455

Have you signed into their account to try to change the password? Enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.

Apple ID - Manage            

Apple ID – Forgot Password