WhatsApp requires both users to have a WhatsApp account, and to do that both users need to have a phone with whatsapp installed (whatsapp web just connects to that phone, the phone is the thing that does the actual messaging).
The only other way that WhatsApp allow communication is through their business API, which you have to go through an aggregator in order to use, eg twilio Twilio API for WhatsApp | Send messages, alerts and notifications on WhatsApp using Twilio WhatsApp Messaging API.
I think it should be possible using that, but keep in mind that with the whatsapp API, the messages have to be sent within 24 hours, otherwise you can only use pre-approved templates. So your helpdesk operators will have to send in a message at least once every 24 hours.
The way I would see this working is, your whatsapp business number is the “user”, and the people that the whatsapp business number is talking to are the helpdesk operators.
There’s a topic here around human handoff that should help: How a human handoff is done in rasa or rasa x
You’ll probably need to build a middle bit to handle the helpdesk operators, so that they can log in and log out, so that you don’t connect them to users while they’re logged out. And since every operator can only talk to one user at a time (unless you have multiple whatsapp business numbers), you’ll need to have some queueing system, and a way to select and connect operators to users, and to disconnect and mark them ready to accept a new user when they’re done, handle telling users where they are in the queue, etc.