There is only one way to delete timers.
Click the ⋮ button in the upper right corner.
Tap on "Edit board".
Tap on the timer for a couple of seconds until the context menu pops up.
Tap on the "Delete" button.
Tap the "Done" button in the upper right corner to save your changes or tap the "Cancel" button to cancel deleting the timer.
Unlike the iOS version of the app, the Android version of the app has a "Cancel last action" function.
This function allows you to undo any completed action in the application.