how to plug a 3 phases oven from the panel
For your question 1:

That was a big label on the MCB circuit 415V Three Phase.
The main concerns are the agent, is he okay?

For question 2:

Yes you can if you know which cable for phase 1, 2, 3 (in this case RYB).
Check for an electrician to make a special plug or wiring especially for 3 phase system.

For question 3: already answered in no.2 answer