Hi @armelynhuldong,
After some digging online I managed to find an English copy of the [link|https://www.manualslib.com/manual/2979509/Siare-Siaretron-4000.html?page=77|service manual (link)|new_window=true] for the Siaretron 4000. It has a section on calibration, and the references to what information is relevant to the flow valve calibration can be found on page 77.
The manual doesn’t have a section on damages via rust, and the section on replacement parents only offers the typical “only use OEM parts”. Additionally
If the rust has only damaged the support brackets for the sensors, you might be okay. However, if the sensors themselves or any connections between them and the other boards have been damaged then that could be the cause of the issue. If the problems are due to rust damage, then you may have to find replacement parts or go to an authorised service technician (as much as I hate to say this, there isn’t any detail on how to source parts from their website so it might be pretty locked down).
I hope this helps.