Hello my lights no longer turn on at sunset. I don’t know how to install the Hello Home SmartAp Could this be installed by the administrator?
Was it just deleted randomly? This may be due to the cutting of off the groovy integration. It may have a new API integration under add a device
Groovy is not being retired until late 2021.
What is the Hello Home smartapp? You have several options for managing lights in the new app. You can use automations, or a combination of automations and scenes, or smart lights. If you really want some fun, you can check out webCoRE for more complex rules. 
Perhaps I got the name wrong but my automation to turn lights on at sunset no longer works. Searching this forum I read that this app is required to be installed.
I believe you were referring to the Hello Home section in IDE.
There are some things you can try:
- check that you are still able to control those lights in the ST app and rule out it is not a problem there.
- install smart lights and create a rule to manage tHe lights to come on at sunset and off at whatever time you choose to see if that resolves the issue for you.
- check that your geolocation is set correctly. Click on More options (3 dots in the upper right of the screen) and select Manage location and look for geolocation on that screen.
To install smart lights, click on the + (plus) in the upper right of the screen and choose smartapp, then locate install smart lights if you don’t already have it installed.
You got the name right. In recent years it has just been thought of as the app that runs Routines but it kept its original name. It included a child weather app that sent out sunrise/sunset events and times for use by legacy apps.
With migration, and for new users, the Hello Home app has been withdrawn and the weather app bolted on to Smart Lighting.
It isn’t required for ‘new’ integrations such as Automations.
I see @jkp has given you a list of things to try.
Thank you jkp, your recommendation worked. All working well now.