Hi 524Now,
Thank you for using the Apple Support Communities! It's my understanding that you're unable to determine the password needed to mirror your iPhone to your TV. I can help.
Learn more about mirroring your iPhone screen to your Apple TV or AirPlay 2-compatible smart TV here: How to AirPlay video and mirror your device's screen - Apple Support.
If you are trying to mirror your iPhone screen to Apple TV, it may require a PIN to use AirPlay. Check to see if you have this enabled by following the guidance in this article, under the section 'Require a PIN to use AirPlay' and 'Set up Device Verification for Apple TV': Manage AirPlay settings on your Apple TV - Apple Support.
You'll also find more help in this article if AirPlay or screen mirroring is not working: If AirPlay or screen mirroring isn’t working on your device - Apple Support.
If you are attempting to mirror your iPhone screen to a smart TV, you will want to reach out to the manufacturer of the smart TV for guidance on the PIN number: Contact a third-party vendor - Apple Support.
Reach back out if you need continued support.
Regards.