My apologies for the delay, we are working to catch up to unanswered threads, and get future threads answered faster.
There is not currently a direct cmdlet to list the routes associated with a connection, but you can get the connection and list the routes associated with it:
$conn = = get-vpnconnection -ConnectionName "your connection name here"
$conn.routes
Now that you can see the routes, you can remove them with the Remove-VpnConnectionRoute cmdlet