How can i install Plugins manually on picore lms

Dear members,
Unfortunately I updated my Synology to DSM7.
DSM7 does not run logitech media server anymore, so I installed picore with lms on a raspberry3.
I love Erlands plug-ins, but you can only install them manually.
I tried with this command:

scp -r /Downloads/CustomClockHelper tc@192.168.9.165:/usr/local/slimserver/Plugins/CustomClockHelper

the plug-ins show up after restarting LMS, but after a reboot of the raspberry they disappear. Can anybody help please?

Thank you