Select the instruments track by track, that is most reliable for basic use.
Right-click the track and go to Programs, then follow the desired path for the desired patch. This works fine for GM sounds.
Patch Select dialogue also works, and can be more customized if you have the synths to suppoert it.

Inserting a program change (patch change) Event on the track itself would be next in my experience.

Coyote synth?

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