To complete the sentence, suitable options could include terms related to information or arguments that influence opinions. Here are a couple of correct answers you could use:
- arguments
- perspectives
- evidence
- insights
So the completed sentence could read as:
"During a collegial discussion, a participant can tweak their own opinion when another person reasons effectively and presents new arguments/perspectives/evidence/insights."
You can choose the one that fits best based on the context you have in mind!