Only hope you have is a bit off the wall:
1) as above - Stick a camera so it can see the display and OCR it.
2) Program the temp to trigger the relay at your warning temp and pick the relay change up.
Section 3-6 has an example of programming the unit but it also checks for a lower temperature so it will need modifying.
Note as this is a ‘C’ model, you only have one relay contact and that may be needed by the plant so you need to check with the plant engineers to see how you tap in and feed an opto-isolator and then to the Pi. Without a lot more plant details I doubt folk would want to advise you on the relay link just in case
Best bet - replace it with a more modern unit that can interface to others...
Need Pi spray - these things are breeding in my house...