SharePoint does not provide a built-in feature to apply Content Organizer rules to existing documents in the Drop Off library.
If you need to apply the rules to existing documents, you may need to manually move or re-upload the documents to the Drop Off library so that the rules can be applied.
See: Apply Content Organizer Rules when Sharepoint receives a new document via email
And: Update document metadata in a library via PowerShell
You can try with PowerShell (edit: UPDATE)
# Load SharePoint Snapin
Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue
# Set the URL of your site
$siteURL = "http://YourSiteURL"
# Get the SPWeb object for the site
$web = Get-SPWeb $siteURL
# Get the Drop Off library
$dropOffLib = $web.Lists["Drop Off Library"]
# Loop through each item in the Drop Off library
foreach ($item in $dropOffLib.Items)
{
# Check out and check in each item to trigger an update
$item.File.CheckOut()
$item.File.CheckIn("Updated to apply rules")
}