Open the Formula Editor

Basically, if you can see a formula, double-click it to edit it. If you can see the place a formula should be, double-click that or bring up a context menu for an object, and choose a command that requires a formula.

To write or edit a formula for a(n) …	Do this to get the formula editor …
Attribute (Define an Attribute by Formula When the Formula Row Is Hidden, Define an Attribute by Formula Using the Collection’s Inspector)	Click the attribute name in a case table or Cases panel of an inspector and choose Edit \| Edit Formula. In a case table, choose Table \| Show Formulas to display the formula row under the attribute names. Then double-click the cell under the name of the attribute whose formula you wish to edit. In the Cases panel of an inspector, double-click the formula cell for an attribute. Bring up the Context (Right-Click) Menus for the attribute as it is displayed in a case table or inspector and choose Edit Formula. In a case table for an attribute whose values are already computed with a formula (they show with a gray background), double-click any of the values.
Filter for an object (Restrict the Cases You See by Filtering Data)	Select the object and choose Object \| Add Filter. If there is already a filter showing underneath the object, double-click it.
Measure (Define a Measure)	In the Measures panel of a collection’s inspector, double-click the Formula cell of a measure. Bring up the Context (Right-Click) Menus for the measure as it is displayed in an inspector and choose Edit Formula.
Plotted function (Plot a Function on a Graph) or a plotted value (Plot a Line at a Given Value on a Graph)	Select a graph that has two numeric axes and choose Graph \| Plot Function. Most graphs that have at least one numeric axis can take a plotted value. Select the graph and choose Graph \| Plot Value. For an existing plotted value or function, double-click its formula.
Slider (Define a Slider by Formula)	With the slider selected, choose Edit \| Edit Formula. In the Properties panel for a slider, double-click the Formula cell in the first row.
Value in a statistical object (Use Sliders to Vary Summary Information in a Statistical Object)	Click in the value whose formula you would like to create or edit. Choose Edit \| Edit Formula.