A 70-year-old woman with a history of heart failure with reduced ejection fraction (HFrEF) is stable on ramipril, bisoprolol, and furosemide. Her eGFR is 50 ml/min/1.73m2 and potassium is 4.2 mmol/L. She remains symptomatic with NYHA class II symptoms. According to NICE NG106 (Chronic heart failure), which medication should be considered next to improve prognosis and symptoms?