The use of Amazon Prime Video account PINs is optional and is under the control of the account holder.
Amazon article re PIN management: https://www.amazon.com/gp/help/customer/display.html?nodeId=G2NLF42JTSS9SDK3
If that doesn't help, have you tried logging out of Prime and back in again?
In Prime Roku app:
Go to menu, left side of screen
Scroll down and click on Settings
Scroll down and click on Sign out, follow prompts
When signed out, system will return you to Prime home page
Go to menu, left side of screen
Scroll down and click on Settings
Scroll down and click on Sign in, follow prompts
Sign in again with your Amazon Prime email and password
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X