Welcome to Nico. I don't know how much experience you have with dismantling your M, so please forgive me if it seems I am telling you what you already know.
The seat temp controls are not actually wired directly to each front seat. They are individual switches with matching connectors that are woven into a huge bundle of wires in a sort of 'main' harness inside the console.
Lift the armrests to get them out of your way. Then lift out the cup holder insert.
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Next, partially close the cup holder door and grab hold of it while lifting upwards.
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You will see 4 screws that hold the switch assembly in place. Remove these screws ands you will see each individual switch. If you flip the assembly upside down, you can gently push each switch out the front. They each should have their own wired plug. If your switches are not plugged in, and you don't see any loose plugs laying around about the floor, Your issue is probably larger than just switches. There may be something larger missing like a main harness.
If you notice, my assembly has a switch for "snow" found only in AWD models. I have a RWD model and my car came with a generic plastic 'blank' shoved into that space. I have a thing about seeing 'blank placeholders' so I bought a snow switch form an Inifniti parts shop so that I have no 'blanks' showing. There was an actual wired plug for this switch already in my console and I attached it so all the switches light up at night. The snow switch will light when activated. It just has no effect because at the other end of that harness there is no AWD system, LOL.
If your switches are plugged in, you may need new switches. Instead of buying the switches individually, I recommend buying a used switch assembly that already has all the switches included:
https://www.ebay.com/i/263820252527?rt= ... 3820252527
Hope this helps