Change the mobile number of the user in the Phone section.
The screenshot below shows you the fourth to fifth steps.
However, if you're unable to change the mobile number on your end, I recommend getting in touch with our Customer Support Team. They have the necessary tools to help you update the user's contact info.
Aside from the mobile number, you can also change your email, business name, or VAT # in the program. It helps you make sure the details are up to date on file. For more information, visit this article: Updating Business Info in QBO.
I'll be right here to help if you need further assistance. Take care always, @tanya6.