There are some other threads on this topic (example) that seem to be helpful.
I think the best thing you can do is hire a lawyer with expertise in GDPR and start working with them toward compliance.
Don’t let the nearness of the deadline make you freeze (or despair). There are many businesses who are just waking up to this and starting the process now is the best thing you can do.
Another helpful link: https://www.digitalmarketer.com/gdpr-summary/