Say the app is already on the phone and something nasty has already landed. What do you actually do in the next hour? I have been through this with a niece, and here is the order that worked.
Step 1. Do not delete anything yet
Instinct says wipe it. Resist that. Screenshot every message first, and capture the timestamp visible on screen along with the message itself. If this escalates to the school or the police, deleted messages are gone forever and unusable.
Step 2. Pull the link down immediately
Open the child’s linked profile and remove the NGL link from the bio and from any active story. The inbox goes quiet within minutes because nobody can reach the form anymore. This single action stops the bleeding faster than anything the app offers.
Step 3. Report inside the app
Long-press the offending message and use the report option. Then block. Understand the limit here: blocking works on a device signal, so the same person can return from a different phone.
Step 4. Escalate to the platform the link was shared on
If the link sat on Instagram or Snapchat, report the harassment there too, because that platform holds a real account behind a real login. That is where identification is actually possible.
Step 5. Involve the school if the sender is likely a classmate
Most schools have a written policy covering off-campus digital harassment that affects the school environment. Bring your screenshots printed, not on a phone.
Step 6. Watch the kid, not the phone
Sleep changes, dropped hobbies, and sudden refusal to go to school matter far more than any message log. That is the signal worth acting on.