What is the ruling on writing down the names of three colleagues for the manager, accusing them of mischief, when there is no certainty and there is fear of wronging them and experiencing pangs of conscience, and what should be done about it?

You must repent to Allah Almighty and seek forgiveness from your colleagues whom you accused of theft without proof. If you are unable to do so for fear of greater harm, then supplicate and seek forgiveness for them abundantly, and do not repeat such an act.