You can either take apart the whole extruder head, or try to loosen the two screws that hold the sensor PCB from the side (which clearly wasn't supposed to work but can save you a ton of time). Taking apart the whole head has the added benefit of being able to clean it thoroughly, which might be a good idea while you're at it. The sensor PCB is connected via a dupont-style connector, so is easy to disconnect. You can then take the bare PCB and perform the SMT-rework;

- removing the old sensors (note their orientation first, as that is missing on the PCB)

- cleaning the pads, maybe adding some fresh solder

- use hot-air or normal soldering iron to attach new sensors. These cannot withstand high temperatures for long, so take care while doing this.