A 68-year-old former smoker (50 pack-years) has chronic cough and exertional dyspnoea. Post-bronchodilator spirometry shows FEV1/FVC 0.60 and FEV1 45% predicted. He has had two moderate COPD exacerbations requiring oral steroids and antibiotics in the past year despite treatment with a LABA/LAMA combination. According to CTS COPD pharmacotherapy guidance, what is the next step?