Since version 6.0 of JChem for Excel, the Help on this function button is available for JChem for Excel functions in the Function Arguments dialog.
It is possible that the No help available notice appears in this dialog.
This can happen when the Jcfunctions Add-in is not enabled in your Excel Add-in list, some installer issues can cause this state.
To enable the add-in manually, follow the steps below:
Open Excel and click File > Options.
Navigate to the Add-ins tab.
Chose Excel Add-ins from the Manage drop-down list and click Go.
Tick the checkbox next to Jcfunctions, and click OK.
Restart Excel, and check if the JChemExcel functions are displayed in categories (as it is described in Use Custom Chemical Functions topic).
Select the desired function, h elp is now available in Insert Function and Function Arguments dialog as well.