@najwan, when you move your email from your on-premises server to Exchange Online, users will keep their existing passwords. They won't need to create new passwords when they first log in to Exchange Online.
The reason users don't need to reset their passwords is because the migration process copies over their existing password information. When they log in to Exchange Online, their password is checked against the same information stored in their on-premises server. This ensures a smooth transition without any password hassles for your users.
In the situation, when you want to change the initial password for users, you can do so after the migration is complete. My recommendation is to use the Set-MsolUserPassword cmdlet in PowerShell to reset the password for individual users, or you can use the Azure Active Directory PowerShell for Graph module to reset the password for multiple users, for example it can look like this:
Set-MsolUserPassword -UserPrincipalName email address removed for privacy reasons -NewPassword (ConvertTo-SecureString -AsPlainText "newPassword" -Force)
To reset the password for multiple users using the Azure Active Directory PowerShell for Graph module, apply this:
$users = Import-Csv -Path "C:\Users.csv"
foreach ($user in $users) {
$newPassword = $user.NewPassword
Set-AzureADUserPassword -ObjectId $user.ObjectId -NewPassword (ConvertTo-SecureString -AsPlainText $newPassword -Force)
}
One more recommendation is to use some backup software, in my case it's nakivo, and also keep in mind, that resetting the password for users will require them to create a new password the next time they log in to Office 365.
