This solution describes how to change the wifi network on an existing smart home hub in your SmartThings account.
Please follow the steps:
1. Open SmartThings app
2. Switch to Devices tab or Favorites tab, then find your hub in one of the rooms by swiping left/right
3. Tap on your Smart Home hub to access its page (Example image shows the hub is Harvard US, you may have named it something else). 
4. Click on the 3 dots in the top right corner and then on "Settings"
6. Click on Change Wi-Fi Network
7. Press and hold the reset button until it blinks yellow
- If it changes back to solid green, give it a few more seconds.
- You may need to attempt this multiple times (if the LED rebounds to blue LED) until the flashing yellow continues to flash on its own.
8. Click Next when you've confirmed your hub is flashing yellow. 
9. Scan the QR code (located underneath your hub) - If it isn't scanning, try turning on flash which should be available for you during the scan as a flashlight icon.
10. Press Connect
10. Select your Wifi and enter the password
11. The change from Wifi is complete.