翻译“放回原处”，直接用put back就可以了。

Please put the chair back. 请把椅子放回原处。

When you've finished, please put the cassettes back. 你听完后，把磁带放回原处。

如果要准确一点，也可以加上where it belongs。如：

Please put the chair back where it belongs. 请把椅子放回原处。

When you've finished, please put the cassettes back where they belong. 你听完后，请把磁带放回原处。

也可以用where it was (before)。如：

Please put the chair back where it was (before). 请把椅子放回原处。

When you've finished, please put the cassettes back where they were (before). 你听完后，请把磁带放回原处。

当然，如果主句是过去时态，where从句的时态也要调整。如：

When he finished, he put the cassettes back where they had been. 他听完后，把磁带放回了原处。