The Wolf of Walmart

I've designed an oven and am trying to calibrate the PID controller. I have a J type thermocouple and am using the Analog Discovery 2 to log the millivolt reading at the terminals of the PID controller. I see in Waveforms that I am able to use functions on the thermocouple signal. I would like to make a function that converts the signal to a temperature so I can plot and compare the temperature to set point. The company that manufactures the thermocouple has a chart for emf/μV but I am not unsure how to turn that into a function. I contacted an applications engineer from the company and he was unable to help me. Searching online isn't turning anything up either. Is what I am trying to do possible?