Currently, UI allows selecting only one date range per report. You would need to view the Activity Reports for each date range separately. However, If you are willing to view the reports for the complete date range, you may try using Graph view for the complete time range.
Report Settings
If you would like this requirement to be productized in the future, then we recommend that you submit this as a feature request through the below link
https://forums.adobe.com/community/experience-cloud/marketing-cloud/target --> Submit an idea
This has the visibility of the product management team and would help get the feature prioritized if more users on the forum support the idea.
Cheers !