Choose Tools tab→Variables group→Variables 
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Position the cursor over the Value cell for the variable you want to edit, and then click.
Type a new value, and then press Enter.
Tip:
You can use the Filters button on the Variable Table to control what types of variables are displayed.
In ordered, you can only edit the value for variable cells that have a white background. Cells with a gray background are read-only.
In synchronous, you can only edit the value for Value cells that have an Edit Dimension button. Cells with a gray background are read-only.