1. Identify a commitment you have made that is not benefiting the project.
2. Consult with the project manager and/or supervisor whether this activity can be removed from your list.
3. Identify someone suitable to deal with this task. Seek advice from your manager when in doubt.
4. Once you've secured management authorization, transfer the details of your commitment to that person.
5. Advise the person to whom you originally made the commitment that the task has been reassigned to another person, and explain the reason for this action.
Depending on your role and authority, you may be able to deal directly with the person to whom you made the commitment, and you can resolve the conflict without involving other parties.
There's no magic formula for undoing what's done. But by breaking such commitments in this professional manner, you are renegotiating the terms of your commitments and earning trust and credibility.