To change the value of a logical variable, use the EVAL debug command.
CL declarations: DCL VAR(&LGL1) TYPE(*LGL) VALUE('1')
DCL VAR(&LGL2) TYPE(*LGL)
Debug command: EVAL &LGL1
Result: &LGL1 = '1'
Debug command: EVAL &LGL1 = X'F0'
Result: &LGL1 = X'F0' = '0'
Debug command: EVAL &LGL2 = &LGL1
Result: &LGL2 = &LGL1 = '0'