I don't think it matters what plug to take out, but I think it recommended to take out the one by the thermometer controls and leave the other one in until day 18.
My first incubator was a 9300, so it's a little different I realized. I found a Youtube video on yours here:
Maybe you've seen it...
Speaking from some recent trials and tribulations with this incubator!
Here's what I learned from my first 2 batches of incubating eggs this year with this model:
1. Temperature and humidity are SUPER important. You will need to calibrate your thermometers and hygrometers. Definitely use more...