How to remove attribute from an Objectitem

Hi,

I am developing an assistant where when the user sets 'X' on the attribute for the device, It should add the attribute to the device and when the user sets ' ' on the attribute for the device, It should remove the attribute from the device.
I am able to add the attribute to the device but unable to remove the attribute from the device. I found out the issue was because the device only reads the attributes that are in System Attributes but does not read the attributes that are in other tabs as show in image1.

Which is maybe why I can't use the remove method as below: Because I want to remove attributes that are in other tabs of the device.

item.Attributes.Remove((AttributeId)attr.ID);

Is there any way to access all the attributes from an object or any way to remove attributes that are in other tabs of the device?

Thank you.