At this point, the Office 365 service only allows for the retention of audit entries for 90 days. Can you provide us more information regarding your requirement to keep logs for 3 years. Is this a legal obligation? Please provide details around the specific audit entries you would like to retain for an extended period of time.Anonymous commented
O365 Audit logs are now available beyond 90 days for E5 customers. This feature is in Preview. More details here - https://docs.microsoft.com/en-us/office365/securitycompliance/search-the-audit-log-in-security-and-compliance#before-you-begin
"The one-year retention period for audit records for E5 organizations (or E3 organizations that have Advanced Compliance add-on licenses) is currently available only as part of a private preview program. To enroll in this preview program, please file a request with Microsoft Support and include the following as the description of what you need help with: "Long-term Office 365 audit log private preview".