You have to move the following macro DFHBMFSE to the Attribute field of that particular Variable.
MOVE DFHBMFSE TO CUSTA
You can also turn the MDT on by program, when you send a field to the screen. Using this feature ensures that a field is returned on a read, even if the operator cannot or does not change it. The FRSET option on BMS SEND commands allows you to turn off the tags for all the fields on the screen by program; you cannot turn off individual tags by program. If you are using terminal control commands, you turn on a bit in the WCC to turn off an individual tag.