What should someone do who owes less than a dollar to a person he doesn't know, due to the long passage of time and war, should he give the amount in charity to the poor?

If you despair of reaching the owner of the money and you are overwhelmed by the belief that you will not be able to reach him in the future, then give it in charity on his behalf to the poor. If you meet him later, inform him of what you did; if he approves, he will have the reward and you will be absolved. Otherwise, you must return the money to him, and you will have the reward for the charity.