Activate Preview Generator on Synology NAS

Hi guys,
I would like to know how it’s possible to start the preview generator service and add it to the cron jobs on a nextcloud which is running on synology nas.
The problem that i have is, that i’m unable to run occ in my terminal and i’m just not able to find a solution for this.
It would be really nice to see this service work on my nas, because i use it mostly for picture sharing.
Thank you in advance

Edit: if it would be easier for you to do this via teamviewer (etc) just write please