At a basic level, I suggest using an ABM campaign. Do you have 6Sense or Demandbase? If so you can target anyone from that account, running some paid and social retargeting ads. I suggest building a personalized landing page that has that company's logo and name on it, showing how you have success solving their pain/generating revenue today and speaking to how expansion with X product can help more. I'd also suggest AB testing the landing page seeing which messaging or positioning of form, etc. performs best.
If you have an account management team, CTA would be to book time to explore X with your AM and have their calendar embedded in the page.
You can also run a direct mail campaign and drip emails from AM team to these accounts offering a gift with meeting (Marketo used to do this when i was in a Hubspot house with champagne using Alyce). We do it at my company for top tier clients as well using Sendoso.