First, install the 1.2 firmware from here: https://pichenettes.github.io/mutable-instruments-documentation/modules/plaits/firmware/
Important: Like me, you might not get the up/down and new orange modes unless you first do this:
You’ll have to press both A buttons simultaneously (not hold them but not tap them either; just a generic medium press) before you have the ability to scroll through the presets sideways. Then you’ll have to press left or right to get to the Orange models. — Toccata
Then, open this editor: https://pichenettes.github.io/plaits-editor/patch_bank.html
And drag and drop DX7 patches from here: https://yamahablackboxes.com/collection/yamaha-dx7-synthesizer/patches/ – for example, the original 32 patches that shipped with the DX7 are found in ROM1A and ROM1B – here’s a nice demo video of those – https://www.youtube.com/watch?v=F3rrjQtQe5A
Props Synth Dad for this demo: https://www.youtube.com/watch?v=Y2fxCdsYkss