when, in Layout Mode, you go to create a new Layout, FileMaker asks you from which Table it has to show the records.
If the layout is already created, you can change table with:
Layouts >> Layout Setup... >> General >> Show records from: XXXX
where XXXX is a list of available TO ( Tables Occurrences )
I'm a relatively new user of FileMaker and this issue had me stumped as it did prakashroy. Your response resolved my problem!