The available fields are defined by the command statements. If it is not lised under either of the commands then it is either excluded in the command itself or it was renamed.
Go into Database Expert under Data tab
Command1 and Command2 should be listed
Right click on eitehr and select View Command
from here you can see what your sources are and what the origianl fields from the sources are. You can also edit the command to include another field from said tables.
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