DIY Mono/ Stereo switch box

[thankyou]

Hey Guys i would like to build a Mono/ stereo switch box.
with 2 mono TRS inputs and 2 Mono TRS output. and a toggle swith to switch between stereo and mono.
i know its a simple project but i'm just starting electronics and i tried to put it together but i have some problem to get it to work.

Does someone has a simple diagram that i can follow?

Thank you very much
Thankyou.