If this is the issue you are running into, all you would have to do is power your iOS device off, wait a minute, power your phone back on and try again. But let us ensure you are having the grayed out "Next" button issue.
The issue is very straightforward to resolve but first let us ensure the issue you are experiencing is, indeed, the gray "Next" button issue.
Assuming all permissions have been granted, this issue has been happening exclusively on iOS devices running some version of iOS 13.
Furthermore, here is what the issue looks like (the "Next" button has been circled in red to draw attention to it):
If this is the issue you are running into, all you would have to do is power your iOS device off, wait a minute, and power it back on.
Once your phone is up and running again, power the bulb off and then back on.
Then, open up the Sengled Home app and try again.
Ensure your phone has given the Sengled Home app the "Location Services" permission.
On your iOS device(s), this can be found by tapping on "Settings", then "Privacy", then "Location Services", then "Sengled Home". Make sure Sengled Home's Location Services permission is set to "While Using the App".