Air carrier Captain reported during climb the cabin altitude began increasing abnormally. Captain stated the First Officer had changed the pressurization setting after it was initially set and had forgotten to re-set correctly.

Narrative

Aircraft X. ZZZ-ZZZ1; we had a pressurization issue in which [we advised ATC]. Captain was the PF (Pilot Flying) and the PM (Pilot Monitoring) was FO (First Officer). Once we got to the aircraft we began our checks. Which the CA (Captain) performed his final cockpit scan. Though it is not on the CA's final cockpit scan. With the experience through the years; I always check the manual pressurization knob to ensure the knob is in the 'DN' position. Which at that time; it was full counterclockwise 'DN'. At the beginning of the trip there was several things going on. Runway XX had a NOTAM for Runway XX FICON 6/2/5 25 PCT WET; 60 PCT 1/4IN WATER; 30 PCT WET OBS AT Date/Time; #4 brake indicator pins were close to wear; the aircraft had to be de-iced and there was an issue on getting the clearance with the FO. Due to the busy work load; I talked to Dispatch couple of times for obtaining the APA numbers for the NOTAM runway and Maintenance for the #4 brake as well as coordinated with ops for de-icing. While we were getting ready to de-ice; the FO called up the FA (Flight Attendant) to tell him we were beginning de-icing and when he got off the phone the FO stated he had a hard time hearing him.While climbing through 13;200 ft.; we noticed the cabin altitude was around 8;700 ft. and climbing. When I saw this; the statement refer to QRH cabin altitude in amber was cut off by triple chimes 'CABIN'. I immediately asked the FO to request a descent to 10;000 ft. FO asked me if the emergency descent checklist should be ran and I stated yes. We alerted the Center of the problem and told them that we will get back to them if we needed assistance. Once leveling at 10;000 ft.; the I noticed the cabin altitude was at 9;500 ft. At that point; I radioed Center; [requested priority handling] and requested a descent to 8;000 ft. The altitude was granted; descent was initiated; FA and Dispatch notified. Once leveled at 8;000 ft. we set up and reviewed for visual approach to Runway XXC and went through the rest of the normal checklist. When we were caught up with everything; I started troubleshooting in my mind the pressurization issue. The first place I looked was the pressurization controller to see if there was error codes to report back to Maintenance as well as the AUTO/MAN switch position to ensure the controller was in fact AUTO. After looking at the pressurization controller; I inspected the manual pressurization control knob and discovered the manual pressurization control knob was in the 1 O'clock position. The knob was turned back to the 'DN' position and normal pressurization resumed. Asking the FO how that happened. He told me that while trying to adjust the volume to hear the FA in ZZZ1; that the knob he turned and forgot to place knob position back to 'DN'. After FO admitted to turning the switch; I explained that the only way that the volume for the intercom can be adjusted; is through the PA amplifier in the forward nose compartment. The rest of the flight was uneventful. Was not aware that after the before start checklist was complete that the pressurization manual control knob was placed in the 1 O'clock position by the First Officer. The only thing would be to do is ensure by both pilots; the pressurization manual knob is in the 'DN' position while taking the active runway for departure.