You can change the first day of any cycle if the app automatically started a new cycle incorrectly; for example, if you added menstruation by accident or if you had mid-cycle bleeding rather than true menstruation.
Here's how to change the first day of a cycle.
Open the Data Entry screen for the incorrect cycle day 1.
Tap the selected amount of menstruation to clear it for the day.
Kindara should automatically resume the previous cycle. You can continue to chart as usual, or you can open the day your period actually started and add menstruation for that day to start a new cycle.
If removing menstruation didn't resume the previous cycle, set new cycles to start manually in your settings. Then you can remove the new cycle from the incorrect day and select the correct first day.