This app was mentioned in 3 comments, with an average of 1.00 upvote
I don't know that nano is installed on Android - it's a GNU program and Android does not ship a lot of GNU stuff. Grab a text editor, there's plenty out there, for example here's one and see if you can use a file manager (with root) to access the file. That being said what you're asking for is akin to piracy.
This is probably not useful, but anyway -- for years, I've used a free Android app called OI Notepad (also available via F-Droid), with the OI Notepad Pebble app. It's ugly and fiddly and only displays ~700 bytes per note, but it still runs on my Pebbles. Unfortunately, to work at all, it requires a companion shim Android app called OI Pebble Adapter, which no longer shows up in a search on the Google Play Store (although the source is available at GitHub). Maybe the APK can be found via some mirror site, though, if you wanted to try it out.