Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services now if the person:
Has trouble breathing, noisy breathing, severe hoarseness, or blue-grey lips
Is drooling or unable to swallow
Has severe chest or abdominal pain
Vomits blood, collapses, has a seizure, or becomes confused
Has a fast, very slow, or irregular heartbeat
Has swallowed potassium carbonate intentionally
Has a significant eye exposure with pain or impaired vision
Arrange follow-up after the emergency period if pain is not improving, an eye remains red or sensitive, a skin burn develops blisters, or coughing continues.
And for anyone, someone who:
you believe has taken an overdose or swallowed something poisonous
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
2
Is any of this happening?
Be seen today
Contact a poison centre immediately after any suspected swallowing, even if symptoms seem mild.
Have the product name, concentration, estimated amount, time of exposure, and the person's age available if known.
Over the following weeks or months, seek prompt medical assessment for difficulty swallowing, food sticking, repeated vomiting, weight loss, persistent chest discomfort, or coughing during meals.
These can be signs of scar narrowing rather than a new poisoning event.
The article also says
After skin or eye contact, start rinsing before making the call.
Do not delay first aid while searching for detailed product information.
Every sign above is quoted from the sofidex article on Potassium carbonate poisoning. If you are not sure, err upward — it is always reasonable to be checked.