Revisiting old projects is a great way to improve your skills and reaffirm and contribute to your overall progress as a coder.
A previously completed project that fulfilled its purpose at the time it was finished but has since remained untouched can be a goldmine for improvement. Re-assessing old code after some time has elapsed can help you see places where there is room for improvement, whether in structure, approach, or a different approach to a problem.
It's easy to make mistakes early on as a beginner (because there ie still so much to learn), but these missteps are easy to spot later on when you have more experience. Taking a fresh look at an old project gives you an opportunity to update it with solutions and gain confidence in applying the coding concepts you employed as part of the fix.
As a developer, supplying and responding to constructive criticism - whether your own or others' - is a valuable ability, and practicing on your past projects is a great way to show you have the focus and self awareness to do so.
By reworking old code that worked but wasn't ideal to be more compatible with your language (Swift should be Swifty, which means no reliance upon hard-coded values, etc) to be DRYer, more efficient, and better structured, you demonstrate an ability to look at your work objectively and see where it requires improvement.
As developers we always strive to learn something new, and putting that knowledge into action by integrating it into an existing project is also a great way to demonstrate it. For example, I have reworked two projects from an original MVC (Model View Controller) design pattern into MVVM (Model View ViewModel) over the past few months, in order to cement MVVM into my mind and simply the two apps I worked on.
If you have old projects that are sitting around gathering dust, you may want to consider revisiting a few of them as well - they are a great opportunity to demonstrate your progress, practice self-critique, and put new knowledge into practice.