There are 2 ways to edit a draft in Canary for Android -> You can edit the saved draft via the 'Drafts' folder OR You can edit minimized draft via compose.
To edit a minimized draft via compose,
1. Tap on ‘Compose’

2. Select ‘Edit : <draft>’

You can also edit the saved draft via the 'Drafts' folder on your Android device.
- To do this, Open 'Drafts' > Tap on the message you want to edit > Tap on the 'Reply Button'.
