Hello @TM_Ire,
Welcome to the Klaviyo Community!
I would suggest taking a look through our Integrations Directory to see if either Klaviyo or your CRM Software program have a developed an integration with Klaviyo. If one is not available, then you can still connect your CRM software to Klaviyo by creating your custom connection between the two by via API.
To leverage Klaviyo’s API to create your custom integration, I would suggest taking a look at the following Help Center articles and documents Klaviyo offers on this subject:
Similar to leveraging Klaviyo’s API and creating a custom integration, you can further leverage the API to make routine post requests to pass in your historic sales data to Klaviyo. Another option available to importing historic data and events to Klaviyo would certainly through a manual .CSV import. Instructions for this process can be found in the How to Manually Import Historical Event Data Help Center article. This solution can further be automated by using Zapier as a medium as it does support connecting Google Sheets and Klaviyo to post events and data.
It may also be helpful to reach out and speak with a developer you are familiar with or finding a Klaviyo Partner who can further assist you with these custom solutions.
I hope this helps!
David