mattermost is taking over my computer, help :(

Im a total absolute noob at linux, i got pop os, and now all that starts after ive logged in to the OS is mattermost app. There is no way to shut it down through the interface. Usually mattermost do not want to shut down completley for me and runs in the background, and i solve this by always doing pkill mattermost in the terminal. Now it wont even go to the background but is taking uo the whole screen, so i cant reach the terminal through interface. Ive tried ctrl+alt+T to get up the terminal but nothing happens. It usually doesnt so im not surprised. This all happened after the os wanted to upgrade and then when it was about to finalize the upgrade and reboot an error ocurred. I didnt understand what is was about... Something about source files? I rebooted it myself and then when i logged in this whole situation above faced me. Ive tried to restart the computer several times, same thing happens. What should I do?