The process is automated:
https://strava.zendesk.com/entries/20959312-flagging-a-segment-as-hazardous
You could contact them and ask them to manually overturn the flag, but I suspect they'll err on the side of caution in light of the unfortunate story linked to upthread. Imagine how bad it would look on them if they overturned a flag and then someone died on that segment while chasing a time?
Tbh, I personally don't think descents are really suitable for Strava segments anyway. At least with climbs you're only limited by your ability. With descents, you're mainly limited by how many risks you're prepared to take.
d.