How to change the aspect ratio in obs?

[SpadeZXOXO]

Hi, i run my windows at 1920x 1080 on 16:9 ratio so does most my games except CSGO i play cs on 1440x 1080 with 4:3 ratio whenever i try to stream on yt theres black bars on the right side of the screen. i tried changing the output resolution in video settings from 1920x 1080 but it only made it look worse. thanks in advance
P.S I'm new at this sorry if i sound stupid