There's a GPO to turn it off, but you'll need to download the latest Office GPO package. Here's a PowerShell script if you're running an RMM tool - it'll need to run as user:

Function SetRegistryKey($RegistryPath, $Name, $PropertyType, $Value){
    # Create the key if it does not exist
    If (-NOT (Test-Path $RegistryPath)) {
      New-Item -Path $RegistryPath -Force | Out-Null
    }  
    # Now set the value
    New-ItemProperty -Path $RegistryPath -Name $Name -Value $Value -PropertyType $PropertyType -Force
}

SetRegistryKey "HKCU:\Software\Policies\Microsoft\office\16.0\common\links" "BrowserChoice" DWORD "0"