A 68-year-old man with a 40-pack-year smoking history and severe COPD has FEV1 45% predicted, a modified Medical Research Council (mMRC) dyspnoea score of 3, a COPD Assessment Test (CAT) score of 18, and three moderate exacerbations in the past year despite regular use of a long-acting muscarinic antagonist/long-acting beta₂-agonist (LAMA/LABA) inhaler. According to the 2023 Canadian Thoracic Society COPD pharmacotherapy guideline, what is the most appropriate next step?