Stand next to your friend and have them ask in a nonchalant friendly way, something like: "This is my first time using your lounge, can I bring in my friend who's traveling with me?"
And smile
Be friendly, not demanding or entitled.
Never hurts to ask. If you're in the main threshold in the lobby already and it's dead in the lounge, the desk agent might be generous in wave you in.
Worst that can happen is they say they have to charge you for a day pass. Your call if you think its worth it depending on how busy the regular airport is and how long your time there is.