It's usually untied like this. It can be operated in the settings. You can try to operate it yourself.

Wechat app unbinding mobile phone number method: first open the mobile phone, find the WeChat app from the mobile phone desktop, and open it. After entering the app, click to switch to my page, click the settings option on my page and open it. After entering the settings page, continue to click Account and Security, and click the mobile phone number to choose to change the mobile phone number.