how to update users email if there is no interface in UI

Dont go to database. instead use the power shell to do same

Add-PSSnapin Microsoft.SharePoint.PowerShell
$site = Get-SPSite http://example.com
$web = $site.RootWeb
$user = $web.SiteUsers.GetByEmail("usr@example.com")
$user.Email = "user@example.com"
$user.Update()