How can I convert a 3D SBS video to individual left side video and right side video?
You can use FFmpeg, a free commandline tool to do this.

ffmpeg -i sbs.mkv -filter_complex "split[l][r];[l]stereo3d=sbsl:ml[left];[r]stereo3d=sbsl:mr[right]" -map [left] -map 0:a -c:a copy left.mkv -map [right] -map 0:a -c:a copy right.mkv