I am not sure if I understand the question correctly, but if you have installed the Customer Service Management plugin you can go to the CSM workspace by navigating to https://INSTANCENAME.service-now.com/now/cwf/agent/home :
If you open a Case record from here, you will find a "Propose Solution" button in the top right corner, which will resolve the case. This is out-of-the-box behavior:
After clicking the button, the state of the case is resolved:
