This feature has now been implemented on the Automation pages.

You can now quickly relink the ad group for Inactive and Unlinked ASINs to any active ASIN directly on the Automation page.

Click the dropdown arrow next to the ASIN, and a popup window will display a list of active ASINs within that ad group.

Select the desired ASIN and click the "Link" button to relink the ad group to it.

If there are no active ASINs in the ad group, you can click the "All products" button to browse and select other ASINs to relink the ad group.