How to make a mono-switch on speakers?

Using 2 Arylic Up2Stream Plate Amp 2.1, I intend on building 2 wireless speakers. When I use these speakers together via the Arylic app, one should function as the right speaker and the other as the left speaker. But if I only connect to 1 of the speakers, I would like it to play both left and right channel, so that I don't miss out on anything. How would this be done?
If possible, I think the best way is use the app change the source to mono.
If you want to use a switch, My suggestion is use a DPDT switch and two resistors (1kΩ) to sum the stereo channel to mono.

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Screenshot 2023-08-28 at 10-02-55 Scheme-it Free Online Schematic and Diagramming Tool DigiKey.png