It’s hard to sit back and accept someone else getting the credit for your work … and you shouldn’t have to. So how do you handle it?
Go to that individual and tactfully work to resolve the problem. Consider that this may be an oversight so allow them the opportunity to explain their actions. You might learn that they told the boss of your contribution and the boss failed to mention it.
If you find that they did not give you the credit, ask them to rectify and clarify what each of you did for the project or event. Obtain an agreement from the individual that this will not happen again. Suggest that in the future, the two of you determine how you will present the project and share the credit.
So what if it happens again and/or the person does not want to cooperate in clarifying who did what? Have a confidential discussion with your boss regarding the situation. Explain to your boss what happened and how you attempted to handle this matter with your coworker. Don’t whine! State the course of events and make sure you have evidence to prove that the idea was yours or that you were the one who did the work.
You deserve credit, so don’t be afraid to claim it. In the end, it benefits everyone!