Thanks for the response!
Im using the Endnote plugin for Word 2016 and I can’t find Edit nor Outputstyles…
I can see the three sections Citations, Bibliography and Style but none of them leads me to the Style manager 
Strangely when I choose another style e.g. BMC Pediatrics the brackets are square as they should be, but then the reference list is not in the correct style anymore… Could it be that the Style for J Ado Health is wrong? Or maybe they changed their style, which i don’t think is the case since even the latest publications are with square brackets…