When your table has a field that links to a record in the same table, Airtable does not create a "backlink" field for you the way it does for cross-table links. If you want these backlinks, you must manually create the second linked record field.
These scripts help you maintain these backlinks.
The Button script lets you quickly setup all backlinks for existing records. Run this script from Scripting App.
The Automation Script maintains keep the linked record fields in sync. When you make changes to one of the linked record fields, the automation script adds or removes the matching values in the other linked record field. Use this script in two automations (one for each linked record field).
These minified scripts are not human readable or editable.
You can see a video demo on YouTube.