Hello Megh,
First of all Welcome to the Quick Sight Community.
To apply a relative date filter to two visuals with different datasets in a single analysis, you have several options:
You can create a parameter with the data type Datetime, add a control for this parameter, and then add a custom filter for your date fields in each visualization using this parameter. for reference see here
you may also refer see use case 2 - Using QuickSight parameters and controls to drive interactivity in your dashboards | AWS Big Data Blog
Hope this gives some idea.
Cheers,
Deep