The word “zo” has a lot of different meanings. In this case it’s said at the end of a (difficult or long) task as filler word.

Like “zo, dat is klaar” (that’s (finally) done now), or “zo en dan nu tv kijken” (and now (finally) time to watch tv)
It doesn’t mean “so” in that case. It’s more similar to “hè hè” in that case. An expression of weariness and/or tiredness. And that’s why I translated it to “finally”. “Now this task is finished, I can finally relax with a beer”.

I hope this clears things up for you?