You're correct, that is an ORP probe.
The PM1 module can be used for either pH or ORP, but default configuration is for pH.
You need to disable the pH probe and enable the ORP probe.
Go to the Inputs page.
Find the line that corresponds to the PM1 pH probe, click on it, select Disable, and Update.
Then on the Inputs page, find the inactive PM1 ORP probe, click on it, select Enable, and Update.