Surface Slim Pen 2 doesn't have a barrel button

ISSUE :    Customer cannot use the tool for doing freehand work 

SOLUTION for Windows 10 / Windows 11 

Please try these steps: 
 

There are four Surface Pens and the features of your Surface Pen depend on which pen you have and the device you're using.
 
Here's the link to guide you on using your Surface Pen with Surface Pro Slim 2.
https://support.microsoft.com/en-au/surface/use-surface-slim-pen-2-be5e4f74-572b-49b4-ae0a-b72d9e7b0d7a#:~:text=%20Use%20Surface%20Slim%20Pen%202%20%201,Studio%2C%20Surface%20Pro%20Signature%20Keyboard%2C%20and...%20More%20 
 
Here's the link for more details
https://support.microsoft.com/uz-latn-uz/help/4036281/surface-how-to-use-your-surface-pen  
 
 
With your Surface Pro Slim 2. please make sure you have the latest Surface Updates
Here's the link on how to get the update  https://support.microsoft.com/en-us/surface/surface-pro-2-update-history-9da532d8-2072-b6e1-7865-57fb7b3fffd9
After the update, please try to use the Surface Pen and let us know the behavior. 
 
 
When you press the Barrel button and then draw up and down it doesn't work?
Do you see any options like the sample image below where you can check to "Allow my pen to act as mouse" in legacy applications? This might be different from your end now, but there's no harm in trying. 
 

 
Another way is to check the registry. Please check with Microsoft support to get the legit support service. do not touch the registry when you're not comfortable and not sure of what to do. 
 
Here's what has to be checked .

However, Surface Pro has Windows 10 and yes the only way is to change the registry.
Not really recommended to touch the registry unless you have an IT tech to help or you feel comfortable to change it.