What I would do is get three
stereo 3.5mm (⅛") jacks similar to the picture below and a DPDT toggle switch and mount them in some kind of enclosure.
Connect the two non-ground contacts of the input connectors to each side of the DPDT switch and the common pins of the switch to the output connector. Connect the ground connections of all three jacks together.
If you need a male connector, buy short stereo 3.5mm male-male cables (which the Dollar Store likely has) to make those connections.
Lest the peanut gallery have any comments about using stereo jacks for these connections, the pictures below illustrated that stereo jacks will work for stereo headphones or stereo earbads/headphones having a microphone.
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