Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services or go to an emergency department if you may act on suicidal thoughts, have seriously harmed yourself, have taken an overdose, or cannot stay safe.
If possible, do not remain alone while arranging help.
Get urgent mental health support if you are thinking about self-harm or suicide but are not in immediate danger.
Contact a local crisis service, urgent healthcare service, or a trusted person who can stay with you.
Arrange a routine appointment if fear or avoidance has lasted for months, causes significant distress, or interferes with school, work, relationships, appointments, or everyday tasks.
You do not need to wait until it becomes severe.
The article also says
Seek help soon if you are increasingly relying on alcohol, sedatives, or other substances to manage social situations, or if depression, isolation, or inability to function is getting worse.
Every sign above is quoted from the sofidex article on Social anxiety disorder. If you are not sure, err upward — it is always reasonable to be checked.