Is keeping a small amount (840 Algerian Dinars) in a current account at an interest-based bank considered a sin that necessitates getting rid of it to complete the avoidance of dealing with interest-based banks, and what must be done about it?

If you are unable to withdraw the remaining balance in your account despite trying, there is no sin upon you, as Allah Almighty says: "So fear Allah as much as you are able." As for usurious interest, it must be disposed of by spending it on the welfare of Muslims, the poor, and the needy. It is not permissible to benefit from it unless you are poor and in need, in which case you may take from it only what suffices your need.