I can't imagine a USB-C charging plug. Nevertheless: Missing plugs can be ordered from Targus without any problems. I have already reordered this for two Acer notebooks.
I sent the order directly to Targus as follows:
To: Dock Support EMEA <docksupportemea@targus.com>
Subject: Universal 3.0 DV Docking Station with Power: Missing Adapter Tip (Note: enter the missing adapter type here like USB-C)

Hello
I bought a docking station. S / N: 1707022446, see attachments (Note: enter serial number and attach proof of purchase)
Unfortunately I missing the adapter for a (Lenovo) notebook. Lenovo:.... (Note exact number).
Please send me the missing adapter to my address:

The respective delivery was free of charge within a few days.