Click on the + icon in the values panel of the widget.
2. Click on fx icon to open the formula builder
3. Go to "Functions" tab
4. Select the function you want to use in the custom formula.
5. As count function required a data value, select the data point from Data browser tab.
6. Once the function created has no syntax error, you can click OK.
7. Hit "Apply" to save the changes.
