on system administration module, custom fields, picklist type fields values are not editable.
As an example:
We have created a custom field. Search at the top searching bar for “Custom Fields”
Then choose the table “HcmWorker”:
Then choose the custom field. And go to the section “Values”:
There you have the possibility to add new values and to change the order of the values but you cannot delete a value or edit a value
When you click on “Edit” at the top, you still cannot change anything even with System Administrator Role.
If you want to change these values (which is the picklist of the field), you have to delete the whole custom field and create a new one, which is not practical in the daily business since this field is connected to several other systems through interfaces and also in Power BIs.