Unable to perform mouse scroll down action using Appium python

Hello ,

I am automating one desktop application using Appium python.
In my application I have one dialog and to handle some elements on that dialog , I need to scroll down but unable to do that. Following sketch will provide more details :

I tried with TouchAction methods like :
actions = TouchAction(driver)

But no luck . Error is thown as :
selenium.common.exceptions.WebDriverException: Message: An unknown error occurred in the remote end while processing the command.

Can anyone help me with this ?

I forgot to mention that Appium is also not able to access the scrollbar . I tried by Appium desktop client to identify the scrollbar but no luck.