I just recorded a short jingle on voice memos. How do I move it to ringtones?

You can transfer it to your PC or Mac and convert the file to m4r, then transfer it back as ringtone via iTunes (Windows) or Finder (Mac).

You can also do it directly from the iPhone, without the use of a computer. You can use the Garageband app to import your file as a ringtone. You can download Garageband for free in the App Store.

First, save your Voice Memo in the Files app. Tap the Share button on the audio file you want to move and select Save to Files. Put it somewhere you can find it again.

The actual process in Garageband is a bit difficult to explain. There I would recommend watching a YouTube video.

I found one you can use here:

https://www.youtube.com/watch?v=-e4BLhef-e4

(In the video at about 1:28, select Files where your Voice Memo file is stored, NOT Music)