Go to Customer list/form and click on Menu > Customize
Expand a current field (represented as rows) in the form to add a new field above or below it
Click on Insert Above/Below to add a new field:
Add the label for the field. In the Depends On section (scroll a little down), add the following: eval:doc.customer_type != 'Company'
Click on Update
Go back to the Customer list and reload. Test the customization by creating a new customer and Type Individual.
For more details, refer the documentation.