A 52-year-old man with hypertension is found to have asymptomatic hyperkalaemia (serum potassium 6.2 mmol/L) on routine blood tests. His eGFR is 50 ml/min/1.73m². His medications include ramipril 10mg OD, indapamide 2.5mg OD, and amlodipine 10mg OD. An ECG shows peaked T waves but is otherwise normal. What is the most appropriate immediate action?