すみません、ラーメンにニンニクを追加できますか？ — Excuse me, can I add garlic to my ramen? (Ramen · Shop, Formal — to staff, JLPT N4)

Gesture & etiquette

Point to your ramen (if already served), or make a small "adding" motion with your hand.

Avoid asking for too many complex customizations in busy shops, especially during peak hours. Be polite and understand if they cannot accommodate.