You can update your partner's name in Cupla at any time. Here is how:
Tap the menu icon (☰). Depending on your app version, it will appear either in the top-left corner of the Home screen or in the bottom-right corner of the tab bar.
Tap your partner's name or profile circle (top right).
Tap the pencil icon (top right).
Update the name and tap Save.
The updated name will appear throughout the Cupla app.
Please note, this only changes how your partner's name appears on your device. It does not change their account name.