UpstoxNet is purely a execution library and it is not a TA library. You can code your indicators seperately and integrate with UpstoxNet.
The sample excel is just a demonstration on how to use UpstoxNet.
You can code your indicators in excel using VBA and the same can be called from excel cell.
If you're a developer, you may create indicators in excel and contribute it to public, so that others will get benefited.