QuickBooks 2020 Desktop Pro Username field showing old user

I have a client that uses QuickBooks 2020 Pro Desktop version that signs in with the user "Admin" every time he uses QuickBooks. Sometimes QuickBooks remembers that correctly and shows Admin when he opens it but sometimes it shows another username in that field. He would like to make sure it always says Admin in the username field and never opens with the other username. I was unable to locate anywhere within QuickBooks where it would retain that information. I would appreciate if someone could help out with this issue, thanks.