Here is a PowerShell script that can be used to delete site owners from a SharePoint Online site:

#Connect to SharePoint Online
$username = "user@domain.com"
$password = ConvertTo-SecureString "password" -AsPlainText -Force
$credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $password)

$siteUrl = "https://yourtenant.sharepoint.com/sites/yoursite"
$context = New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)
$context.Credentials = $credentials

#Get the site owners group
$group = $context.Web.SiteGroups | Where-Object {$_.Title -eq "Site Owners"}

#Get the members of the group
$members = $group.Users
$context.Load($members)
$context.ExecuteQuery()

#Delete the members from the group
foreach ($member in $members) {
    $member.DeleteObject()
    $context.ExecuteQuery()
}
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