Depending on whether you organized your LLC in Pennsylvania or elsewhere, you may not have to do anything to "reactivate" the company. In Pennsylvania, you don't have to have any specific activity with the Department of State for up to ten years. Since you first formed your company only three years ago, you probably wouldn't have to file anything with DOS to use the LLC name, but you might have to file a fictitious name application if you plan to use a fictitious name for the company for any purpose connected with your new activity.
You would still have to fulfill PA DOS testing and any continuing education requirements to maintain your brokers license. Check with your licensing board for those requirements.
If you don't file anything with the PA DOS corporation bureau with respect to your LLC in the next nine years, you would have to file what's known as a Decennial Report the next time those reports come due (which would be in 2021).
Of course, as with all of my online answers, my advice is limited by the brevity of your question and the facts provided. Additional information would be required to provide definitive legal advice, so this answer isn't intended to, and does not, create an attorney-client relationship.
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