https://www.advocate.com/utah-trans-snitch-line
Apparently they want you to go into as much detail as you can on the bathroom incident you observed (I guess things like color, smell, shape and texture) and encourage uploading videos of suspected trans people using the bathroom for the Republicans to...investigate.
As for the question, why are Republicans so obsessed with others bathroom behavior? Why do they automatically assume transwomen (who lets be honest are the sole focus of their bathroom bills) will creep into bathrooms to leer at women and girls? Is it really all just the Republicans projecting their fantasies onto the despised outgroup?