Update/Change Site Collection Admin using PowerShell

<# Description:

- Update Site Collection Administrators
- Provide Web Application URL in this script for <WebAppURL>
- Replace <abc\user1>,<abc\user2> with respective user accounts

#>

Clear-Host
Add-PsSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

Get-SPWebApplication "<WebAppURL>" | Get-SPSite -Limit All | ForEach-Object {
Write-Host "Updating site $_"

# Unlock Site Collection
Set-SPSite $_ -LockState Unlock

# Update Site Collection Admins
Set-SPSite $_ -OwnerAlias "<abc\user1>" -SecondaryOwnerAlias "<abc\user2>"
}