How to make the add-on optional at the time of subscription?

How to make the add-on optional at the time of subscription?

The scenario is this, we have a service which has optional add-ons. Like the customer who purchased the subscription may or may not want to get the add-on. In our case if the customer choose the addon we have monetary benefit. In case the user does not want the addon we have less manual work to discuss further with customer. 

Currently the add-on is by default getting bundled into the package so it brings us to create a different plan or loose money or have manual work to reduce the price. 

how to make the add-on optional at the time of purchase?