How to clear Manager attribute in specific OU using powershell?

I'mtrying to clear the Manager name under the "Organization" tab using PowerShell.

I would like to do this for the disabled OU.

Here is the script and error that I receive. Any help would be appreciated. Thank you

Import-Module ActiveDirectory

$OU ="OU=Users,OU=Disabled,DC=rp,DC=com"

-SearchBase$OU |

Set-ADUser-Manager $null –WhatIf

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Windows PowerShell
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PS C:\Windows\system32 Import-Module ActiveDirectory
PS C:\Windows\system32
PS C:\Windows\system32
PS C:\Windows\system32
PS C:\Windows\system32 $OU ="OU=Users,OU=Disabled,DC=rp,DC=com"
PS C:\Windows\system32
PS C:\Windows\system32 -SearchBase $OU |

Set-ADUser -Manager $null –WhatIf

-SearchBase : The term '-SearchBase' is not recognized as the name...