Presentation format

Hi

I am trying to set a presentation format for a custom characteristic that I am added to CUSTS1 service in the ble_app_peripheral example.

I am unable to figure out the code and more importantly, where to insert the code, in order to display the characteristic value as text. At the moment, I am able to see the characteristic value as empty, but I want to set it as readable text.

How do I set the presentation format for a characteristic ?

Thanks,