Adding a new accessory to the Eve App is really easy:
• Go to Settings
• Tap Add Accessory
Follow the steps on the screen to Scan/Enter the HomeKit Code, Name the Sensor and to Assign it to a Room (use the First Run Setup as visual guidance if needed).
Removing an Accessory is equally simple:
• Go to Settings > Accessories
• Select the Accessory that you want to remove
• Choose Remove From <Home Name>