Thank's for help.
I am not sure did I correct understand how to implement this in my case.
On Splunk side a need to configure inputs.conf and server.conf.
The outputs.conf is use on client side (sending syslog device/ universal forwarder etc).
In my case I don't have option to configure password to sendings log from Synology. I Can only import certificate, if ssl is enabled to sending syslog.
I don't really understand why there is password needed. I don't setup any password for ssl. Is it require to set password.