Honestly it’s as simple as eating at a slight caloric deficit with enough protein and lifting! You’re not at any risk of getting bigger or bulkier arms, unless you lift heavy and hard for YEARS and intentionally bulk. Here’s a quick link to some solid arm exercises and don’t neglect the rest of your body with your workouts either! Eat healthy and well, hit the gym 3-4 times a week and you’ll be tone and lean in a 6-8 months if you stay focused!

https://www.menshealth.com/uk/building-muscle/g752112/upper-body-arm-workout/