Using the Level parameter in the Metric level options

Assuming you have OLAP licence,the easiest way to direct to
a particular table is to create a dummy fact on the
table,include the fact in metric and put the metric in
report objects.

This can be acheived by decreasing the logical size of the 
desire table in a such a way that it should be less than 
other tables. AS Microstrategy will look the tale having 
the least logical size and will make a join with that table.