If a 9th grader competed in a division B team when they were in 8th , can they be part of the team if in their 9th grade they have initially competed in one division c tournament and now want to come back to division B team

Possibly yes, based on the information provided. This policy (https://www.soinc.org/start-team/team-size-grade-levels) allows for the student to choose which division he or she is part of - but states "Any student can compete at only one Division level (either Division B or C, not both) at a single school." However, if the 9th grade student only did an invitational (non-qualifying) as a C team member, just to "try it out", she could potentially "switch" to B for qualifying (regional, state) tournaments, and stay on B going forward. Once the C team is left, the student should stay with the B team.