Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Seek emergency help if the young person:
Call local emergency services or go to the nearest emergency department.
In the United States, call or text 988 for the Suicide & Crisis Lifeline.
Do not leave a young person alone when there is immediate danger.
Contact the treating clinician promptly if there is a sudden major change in sleep, behavior, judgment, agitation, depression, or medication response.
New hallucinations, unusual beliefs, or escalating risk-taking also need urgent assessment.
Regular follow-up is important even when a young person feels well.
Visits may be more frequent during an acute episode, after a medicine change, or when safety is uncertain.
Stable patients still need periodic review of mood, sleep, school functioning, physical health, and side effects.
Arrange routine follow-up if symptoms are gradually returning, side effects are bothersome, doses are being missed, or school and family functioning are worsening.
The article also says
Families can watch for the young person's personal warning signs.
These may include sleeping less, talking more, becoming unusually confident or irritable, withdrawing from activities, or falling behind at school.
A written plan should state whom to contact and what steps to take.
Every sign above is quoted from the sofidex article on Bipolar disorder in child and teens. If you are not sure, err upward — it is always reasonable to be checked.