How to change default app in Android for a file type

On the Android phone you may have chosen to Always Open a file with a particular app. This means that from the File Explorer a press on the filename will lead to the file being opened in the default app.

To reset that default to allow a selection from a list of apps, click on Settings -> Apps, select the app and scroll down and press the Clear Defaults button.

Next time you can choose another app when you open the file.