The HUP states that you cannot observe both a particle’s momentum and its mass, because observing it changes one or both of those. So how can you observe something?
You need a particle that affects nothing. Let’s call it Particle A. But you have to be able to observe it. Let’s say Particle B is another particle that emits and absorbs Particle A, causing it to change in mass. But its momentum is unchangeable. So you can observe it with “normal” particles.
You can use Particle A to observe other particles without affecting them. They bounce back, and are caught by a net of Particle B. You can then observe which Particle B changed in mass, and can determine where Particle A reflected to. You can then determine the location of the particle it reflected off of based on angle and the amount of time before it returned.