We advise you search for the owner.
However, if after searching, the owner is still not found to such an extent
that there is no hope in finding him, then the item should be given in
charity. If you are poor yourself, you can keep it for your personal use. If
the owner comes and claims his item after you have given it in charity, then
he (the owner) can demand the value of the lost item as compensation. If he
sanctions giving it in charity, he will receive the reward for that.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai