User Guide:
Once installed, click on the app picker (the 9 dots) and look for Fix My Picklists
The page will display a combobox with all the names (Labels) of objects in your org which have record types. To the left of the combobox there is a toggle which when flipped will show Object API names instead of their names. Once you select an object, a button will appear which if clicked, takes you to the setup page for that object and to the right of that, a new combobox will appear which lists all the picklist fields on the selected object. Field API names or labels will be displayed, depending on the toggle.
Once you have selected an object and a picklist field a matrix of picklist value vs record type will be displayed for the selected field. Valid values are shown with a checkmark. The default value is shown using a bold checkmark in a box. If the combination is not valid, there will be a blank space.
To edit the allowed values for a record type, instead of going through the pain of navigating via setup, just click on the column header for the record type you want to configure. This takes you straight to the setup page where you can configure the field's valid and default values for that record type. Make your changes and save. Note that due to a quirk of Salesforce's setup UI, editing a object's record type's standard picklist field doesn't use a predictable URL but a hidden hardcoded index value. As a result, with standard picklist fields it's not possible to find a reliable way to navigate directly to the configuration edit page. With standard picklist fields, the user is taken to the record type edit page, from where they must select which field they weant to edit
When you return to the matrix, click the refresh button to see the effect of your changes. If you want the page to refresh automatically, then slide the toggle on the right end of the controls and every time to make the tab active, it will refresh the matrix. The auto-refresh is off by default