You need administrator rights in Jira to perform the tasks on this page.
Once you have gone to the Custom fields page (see Configuring the Proxy custom field), click Edit Default value to select a checklist for the proxy to display in read-only mode.
The proxy is not given any default value when it is first added, and must be assigned a default value for it to work properly.
The following page will appear:
Although the drop-down will preselect a checklist for you, you will need to choose the checklist that you want to read information from using the Checklist Read-Only Proxy.