You need to call o2 customer Services on 202 from your handset or 0344 809 0202 from any other phones and speak to an agent.
You may be asked why you want to change, and you are only allowed one change free of charge
Current Phone: Motorola Razr 5g I also have a Planet Computers Gemini
I work in IT as an Enterprise Messaging and Collaboration Tools Administrator (Office 365, Slack and much much more) and manage hardware both Mobile and Desktop / laptop, my desk is a bit like PC World
-- We are all customers and dont have access to any o2 accounts