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 immediately if a baby:
If the baby is not breathing normally, start infant CPR if you have been trained and follow emergency-dispatch instructions.
Do not shake the baby or place anything in their mouth.
Contact the regular care team about increasing alarms, equipment concerns, medicine questions, or episodes that are changing but do not require emergency help.
Seek urgent medical assessment for a first unexplained breathing pause, repeated pauses, new choking with feeds, worsening noisy breathing, poor feeding, unusual sleepiness, or a clear change from the baby's usual pattern.
A rectal temperature of 38°C or higher in a baby younger than 3 months also needs prompt medical assessment.
For a baby with diagnosed apnea who appears well, use the written follow-up and monitoring plan.
The article also says
Place the baby on a firm, flat surface.
Every sign above is quoted from the sofidex article on Infantile apnea. If you are not sure, err upward — it is always reasonable to be checked.