Even the best software cannot fix a poorly captured stack. This user guide strongly emphasizes that
For the expert user, here is the cheat sheet: helicon focus user guide
Select your "Source" (one of the original sharp frames) and your "Destination" (the stacked image). Even the best software cannot fix a poorly captured stack
This is where the magic happens. Under the "Rendering" tab, you’ll see three algorithms. Choosing the right one is vital: helicon focus user guide
Helicon Focus is a specialized software designed to overcome limited depth of field by merging multiple images into one fully focused photograph Core Workflow Import Images
This means you missed a focus slice during shooting. You can try to fix this in the Retouching tab, but the best fix is a tighter step size next time.