Your Leaf app will occasionally ask you to update your Leaf. This is different from updating the Leaf app which you will be doing through the Apple App Store or Google Play Store. This blue card that will show up in your Leaf app will prompt you to connect to your Leaf and download and install the latest firmware version for your Leaf. The firmware is a piece of code that controls your Leaf and new versions will bring various stability and accuracy improvements to the Leaf. So you will be getting the best possible performance from your Leaf in any given moment.
If you are having a hard time completing the firmware update, please check these troubleshooting steps.