How to remove malware causing pop-ups on a business site?

I know very little to NOTHING about coding and such but I do help my client with her business and we need help. It seems there is a piece of malware that has made its way into the coding of her Shopify store and it is causing highly inappropriate pop-ups - we need help removing this asap.

Hey @LLowery

Please share your store URL with password NOT the admin password.

And the issues you are facing so i can suggest you a solution.