お寿司は手でいただいても構いませんよ。 — It's perfectly fine to eat sushi with your hands. (Cultural · Dining, Polite to Host, JLPT N4)

Gesture & etiquette

Reassure naturally with a friendly smile and a nod. You can demonstrate by picking up your own nigiri with your fingers. Additional tip: dip the fish (neta) side into soy sauce — not the rice, which absorbs too much and can break the piece.

At traditional counter-style sushi restaurants (and often at sushi bars generally), eating nigiri sushi with your fingers is not only acceptable but considered the traditional method. Using chopsticks for nigiri can be awkward and may cause the piece to fall apart. Ginger is a palate cleanser between pieces — not a topping.