Cover your bases and do both! Write the letter, then follow up with a text to confirm that you did it and where it can be found. That way you have a date stamp of when you did it, as well as the written date on the letter.

lots of people write or type letters of resignation. hand it to your SM or take it to the computer in the back where they're sure to see it, that's totally fine. she'll make time to talk to you.

The nice thing to do is write a short letter. Doesn't need to be more than a few sentences. The main points are you're quitting. What will be your last day you work, and briefly why you want to quit.

But if you have no need or use for this as a reference you can do it however you want.