Hi there @Add_46032 welcome to 3Community 👋
Yes, you can👍 If you already have the sim all you need to do is log into your My3 account, then go to the user menu top right of the screen. There click Manage Profile and then Manage My Account then at the bottom of the screen you'll see Add Account. All you'll need to do is click Link Three Number and follow the prompts on screen.
If you haven't already purchased the 2nd sim just log in to your My3 account and then go to the shop and follow the steps to purchase an additional sim.
Let me know if you run into any difficulties.
