If you have an unwanted calendar appearing in Cupla, here's what to do:
Tap the menu icon (☰) in the top-left corner of the Home screen. If there is no ☰ on your Home screen, tap More in the bottom-right corner of the screen instead.
Tap Calendar Settings.
Tap Calendar Connections.
Tap the name of each calendar you do not want synced to Cupla — the row itself, not the switch on it. The coloured ring beside the name turns grey and the Share event details switch disappears from the row.
Tap Save.
Where to find the calendar. The screen has three sections. Device Calendars holds the calendars on this phone, grouped under the account each one comes from — a calendar named in Event Details will be here. Direct Connect holds Google and Outlook accounts connected inside Cupla. Other Calendars appears only when Cupla holds a calendar it can no longer see: one from a phone you no longer use, or one from a Google or Outlook account that is no longer connected — for example a work account whose access was removed. It is labelled as not on this device, and you remove it there the same way.
Calendar Connections only ever shows your own calendars. If the unwanted calendar was synced by your partner, it will not be in your list at all: they need to disconnect it in Calendar Connections on their phone.
Please allow up to 20 seconds for the changes to take effect.