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 for severe breathing difficulty, fainting, confusion, coughing or vomiting blood, sudden severe chest pain, or signs of a major allergic reaction.
Do not drive yourself in an emergency.
Seek urgent medical advice for fever, increasing wound redness or drainage, repeated vomiting, worsening chest or abdominal pain, new shortness of breath, or inability to keep fluids down.
The article also says
Contact your team if swallowing becomes gradually harder, eating causes ongoing coughing, you continue losing weight, or diarrhoea, reflux, or poor appetite does not improve.
Every sign above is quoted from the sofidex article on Esophagectomy - minimally invasive. If you are not sure, err upward — it is always reasonable to be checked.