You unhook things the way you added them.
In this case, you need to pass a callable that matches what was added. Normally this is the function name e.g. 'my_function', but for an non-static method in an object, it has to be [ $object, 'method_name' ] where $object is a reference to the object.
How you get that reference though is a murkier subject. Some plugins use singletons, and have instance methods that will get you the object. Some plugins put new ClassName(); at the end of the file creating anonymous objects, making it nearly impossible to get the object reference for most developers. Some use global variables, etc.
Refer to the documentation for the plugin you’re working with, ask their developer support, and remember, 3rd party plugins are offtopic on WP Stack Exchange.