Couple of months may be a very short time to warm up a cold list. Especially if you don't have any existing auto responder sequence / regular email follow ups with the people on the list.

Creating a few segments, and restarting communication would be the obvious first step. Acknowledge your lack of communication and reconnect with your audience. Ask them about how they're doing with their original purchase from you. Offer to help.

Then start content / value driven emails. May be a couple of webinars in between; and social media campaigns.

Slowly raise their interest in your upcoming product. Talk about the pain points, a "hero" story may be.. And progress into your launch sequence.