The original script posted cannot be easily converted to run as an automation by someone who is not experienced with scripting.
If you read the entire thread you can see that several other people have posted scripts, including some automation scripts. If you want to use any of those free scripts, I recommend testing them thoroughly in a sample base to make sure they work the way you expect and you are okay with the configuration of the fields involved.
There are also some paid options presented in the thread.
- On2Air's Action for Same Table Linked Records (requires a subscription)
- My Same-Table Backlinks automation script (one-time purchase)