user abc not found on Synology

[Dr-know]

Hello,
first time user of Medusa. (previous using sickbeard-custom)
I run Medusa in a docker container on Synology.
I bind the already populated folder /tv with a folder on the Synology volume.
when i want to add existing shows and choose the /tv folder i get in de logs permission denied ...
At the Medusa configuration i see the User: abc
I want to trey to give the user abc read/write access to the /tv folder (bind to folder on synology nas) but this user abc does not exist as a Synology user .. how to fix this , ... even trey giving the /tv folder read/write access to "all users" ..

i use the image Version: 0.5.20 (pulled form linuxserver/medusa:latest )