Sign in with your Microsoft account to continue and manage your Remind account.
Each tab (what you are looking at right now) is a public website embedded into Teams. The specific web address of your personal or a chat's reminders tab is practically impossible to guess but it's still public - this is why Microsoft recommends that tabs are protected by a sign in.
Please only use your own Microsoft 365 credentials to sign in. They are the same credentials you use to sign into Teams.