On the transcription results screen, press and hold the text to open a floating menu, where you may choose the option to re-transcribe.

Alternatively, you may tap the three dots (···) located in the upper-right corner of the home page and select the re-transcribe option.

Note: 

Audio must be transcribed first.
If transcription is not performed initially, re-transcribe is not supported.

Please note that re-transcribing an audio file will consume your usage minutes, while re-generating the summary will not consume any minutes.