How can I just remove Mercari device from my iPhone. Without erasing everything

I can’t get Mercari device off my iPhone? I don’t want to erase everything. My daughter wants to use Mercari on my phone, but it keeps saying she can’t because this device is connected to Mercari? I’ve tried to get rid of it? So she can add her gmail to make an account. It keeps saying she can’t cause the Mercari device is connected to my phone?