Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Follow the discharge instructions from the emergency department, poison center, or toxicology team.
People with a minor exposure and no symptoms may only need observation or a scheduled check-in.
Call emergency services for severe breathing difficulty, blue or gray lips, collapse, confusion, a seizure, vomiting blood, sudden severe chest or abdominal pain, or inability to stay awake.
And for anyone, someone who:
Seek urgent medical care for new or worsening trouble swallowing, repeated vomiting, fever, increasing chest or abdominal pain, coughing after eating, reduced urination, or worsening breathing symptoms.
Those with burns, abnormal tests, breathing symptoms, or swallowing problems may need follow-up with gastroenterology, lung, eye, burn, surgery, or toxicology specialists.
At routine follow-up, tell the clinician about pain with swallowing, food sticking, repeated vomiting, reduced appetite, weight loss, cough, or shortness of breath.
These symptoms may point to healing problems that need assessment.
The article also says
To prevent another exposure, keep flux in its original labeled container.
Never store it in a food or drink container.
Follow the safety data sheet, use suitable local exhaust ventilation, and wear the recommended eye and skin protection.
Store chemicals securely away from children.
Every sign above is quoted from the sofidex article on Acid soldering flux poisoning. If you are not sure, err upward — it is always reasonable to be checked.