Presently, RE cannot globally change and/or delete soft credit information in gifts. It's simply not an option. There's a workaround in the knowledgebase that involves creating a dummy constituent, using an import to change the soft credit constituent ID to that of the dummy constituent, and then deleting the dummy constituent, but that's just an overly laborious process that should not be required.

Usage scenario: We use Sphere to process online gifts, and many of our recurring gifts come over through the Sphere connector. When a recurring gift is first created, a soft credit is added to it if the constituent has a spouse (this is default behavior in RE). When the actually recurring pay-cash comes over through Sphere, an additional, identical soft credit is added to the record if the constituent has a spouse (again, due to RE's default behavior). This causes an error when trying to commit a batch, however, so you have to go through each record, hunting for the duplicate soft credits.

Being able to globally remove soft credits on recurring gifts (not the pay-cash, but the original recurring gift) would remove this problem.