Sprout Forms - Can't save front end entry edits
Craft 3

This feature is available in Sprout Forms for Craft 3 (since v3.0.0-beta.22). 

The feature is disabled by default and can be enabled in the Sprout Forms settings.

Craft 2

This feature exists in Sprout Forms for Craft 2 via the enableEditFormEntryViaFrontEnd config override.