If this bBox is of the instance at the current level of hierarchy, you can search the instances for a matching bBox. Something like:
setof(inst hiGetCurrentWindow()~>cellView~>instances inst~>bBox==myBoundingBox)
If the target bBox is defined at the current level of hierarchy for an instance at a lower level, you can use dbProduceOverlapInst if this is the only instance which occupies the area defined in the bBox, and has the same size bBox, at a certain level of the hierarchy. I would down size the bBox first so that instances who's bBoxs abut the target one's bBox are not reported. Or better yet, upsize the center point of the target bBox by one grid. If multiple instances are found, compare the size of the bBoxs of the found instances to your initial target bBox, or transform the points of the found instances' bBoxes back to the top level to match the target bBox coordinates (this is trickier and only necessary if there could be multiple instances found with the same size bBox, but different origins).
If there are multiple instances reported for either of the above 2 methods, you'll need to know something unique about the instance to qualify its selection. For example part of the instance or cell name, terminal names etc.
Hope this helps.