Volta confusion...

Hi Peoples - I am quite new to MuseScore; - I'm trying to achieve volta(s) such that (e.g) in SATB the 1st run will give S & T voices only and the repeat plays only A & B... and cannot procure the desired effect...
Yes - I've been through the Help on voltas.... but am still baffled.... your suggestions, please & thank you.
John