Currently, we are able to Edit the "Resolution" field to set some value but we are unable to clear the value of the "Resolution" field.

Suggested Solution:

It'd be good if we can clear the Resolution using Automation Rules or if we can set the value to 'None'

Workaround:

We can achieve this using the post function as mentioned in this KB for 

• How to clear the resolution field when the issue is reopened