When you need support.
capella-scan is not recommended for manuscripts.
At first try out different scanning settings:
Things will be more difficult in case your score is a pale photocopy...
Obviously the shape of this symbol does not correspond to common standard.
You have probably scanned a grayscale image and now have to adapt the gray level value (see user guide or program help).
For this edition strongly deviating from notation standard the same is valid than for manuscripts: A secure and complete recognition is unfortunately not to be expected.