I have a iPhone 7 that I want to take off of my account and put my dad’s Sim card in how do I do this

If you forgot the Apple ID (iCloud) 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  *      

If you are giving the phone to your Dad, you might want to do the steps in the article below to make it 'his' phone.

Selling/Giving Away Device.  *

Click on this link to read what to do "If you forgot your Apple ID [Account] 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

What to do before selling or giving away your iPhone, iPad, or iPod touch "Use these steps to remove your personal information from a device, even if you don't have it anymore." Click here --> https://support.apple.com/HT201351

[or if you received one that had not been erased]

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

Learn which size SIM card your iPhone or iPad uses - Apple Support - https://support.apple.com/HT202645

Remove or switch the SIM card in your iPhone --> https://support.apple.com/HT201337