A 68-year-old man with hypertension presents with new-onset nonvalvular atrial fibrillation discovered on ECG. He has no valvular disease, no mechanical valve, and an eGFR of 78 mL/min/1.73 m². CHA₂DS₂-VASc score is 2 (age 65-74 and hypertension). What is the most appropriate next step to reduce stroke risk?