Not sure I understand ... have you deleted the Aeration sheet, or not?
If you have, then the parameter (manipulated variable) "y_S" of the control block should become enabled in the Block Details pane, which then allows you to edit its value manually.
If not, then "y_S" can only be changed through the slider on the Aeration sheet - and being a manipulated variable, this can be done also while the simulation is running.