How to add service UUID to advertising data of implemented by Silicon Labs adapted GATT service

Answer

Steps to adding a service UUID to advertising data of implemented by Silicon Labs adapted GATT services

The implementation of supported adapted GATT services in application firmware using Simplicity Studio IDE is enabled from *.slcp file of the project [Bluetooth] -> [GATT]. Once the developer selects the service, the source code with associated functions will be generated by the Simplicity Studio. However, in some cases the developer might need to extend the functionality of the generated service and add new functions. Example of such new function is a advertising of service UUID.

To add the service UUID to advertising data using [Bluetooth] -> [GATT] configuration, select the service and install it. Once is installed, click on [Configure] blue button in the top right corner and after the configuration is opened, select [</> View Source]. It will open XML file for the service. 
Set service advertising to "true" as follows: service advertise="true". Save the XML file and close it.

After rebuilding and loading the project firmware, the peripheral device with be advertising service UUID. It can be tested with EFR Connect or nRFConnect BLE applications by reviewing the information in the advertising packet.