Use the following database script to update the admin user’s password to lowercase ‘b’ after transitioning from SHA1 to SHA512 as part of security hardening in Sitecore 10.3.1. Execute this script in the core database.
Update [aspnet_Membership] set [Password] = '2hwfEqtM7gDFekQaV/IOkog5DFmxRtywvUsRJqRf7j82Ns3pUkiu/WohjLk8mIV2+7MjXdMeO9MgAUjildTLtg==', [PasswordSalt] = 'ETJOU1+PX4CwEOw/eN3F6Q==' where [UserId] = (select UserId from [aspnet_Users] where UserName like 'sitecore\Admin')