Rebind phone number

Hello, I had an account in the app. Then I got WeChat and decided to create a new account bound to my wechat. It worked. But then I wanted to answer to a message and I 've been asked to rebind my phone. As you can see in the picture. My phone was actually bound to the previous account. I then wanted to unbind. Problem is I cannot find what to type in the box to unbind the phone to the previous account. I even deleted the old account. But I'm still asked to unbind from the deleted account... Anyone knows the exact text to type in the box? Every try, I get : enter the exact keyword.

Thank you for your help