How can I make system message from server side?

How can I make server sided system message? there is local script way but I don’t want to use that, I want to manage system message with one server sided script.

It depends on what you want to do. If you want to make a message from StarterGui you will need to use both a local script & script & add a remote event to make it server-sided.

Put a String Value in replicated Storage, and just change that string value from a server script. Then on the local script you could do something like this:

local StringValue = --define here
local Textlabel = --define here

       Textlabel.Text = StringValue.Value