Just wanted to check if you did the "Sync now" part in step 3.?
3. When e.g. "SureLock Kiosk Lockdown" has installed properly you have to click "Sync now" either on the device's end (open Miradore Online client and tap Sync now) or in Miradore Online's UI (go to the Devices view > select device > click Sync now in the Action column). This action updates devices app inventory in Miradore Online so the launcher app will be available now.
The list of available launcher applications is created based on the inventory data coming from your devices. So you need to have the application installed on one device and the device scanned, which then adds it to the list.