@CameronTCD
Hey there. So, you are definitely on the right track with the table. I'd suggest making a translation table in Excel or something that has the codes and the actual names.
You'll probably want to start with a Recurrence trigger to schedule the run for once a week on Mondays (or whatever you choose).
Follow that with a Get List Items from your SP list. To shorten the list, you can use an OData filter to only grab items that have a value in that field with a length of 3 (or whatever the length is). Search for OData, and also check out this article on functions, specifically 'Length' might be the one for you. It's mostly like working in Excel, so don't worry if you don't like 'code'.
From there, you want to look at each item, right? So start an Apply to Each loop, and get the corresponding name from your table. For this, you can use a "Filter Array" to grab the row of your translation table that has the matching code.
After that (and still inside your Apply to Each loop), use the Update Item to update the field to the name instead of the code.
That should get you started. Give it a go and keep us posted, we're happy to help out along the way.
-Ed-
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