Minichat Keeps Auto-Logging Me Into a Banned Account That Isn't Mine

I logged into my cousin's Minichat account from my own phone. I wanted to help temporarily because my cousin's phone had broken. Afterward, my cousin's account got banned, but this account remained active on my phone as well, and since that day, I haven't been able to use the app properly.
Even though I've uninstalled and reinstalled the app on my phone multiple times, whenever I open it, it automatically logs me into my cousin's banned account. Because of this, I can't log into my own account, under the username "Veysel," at all. This problem has been going on for about 4 days, and I'm unable to use my account.
I am requesting that Minichat completely remove the connection to my cousin's banned account from my device, and take whatever steps are necessary so that I can log in on my phone only with my own account, "Veysel."