Is there a way that I can make a function that can fire from all server scripts?

Okay this is rather simple

_G.FunctionName = function(Variables) -- Define the function
    -- Whatever you want to do
end

In another script

_G.FunctionName(Variables)

This is fairly simple to do. And that is using a ModuleScript. To simplify things; a ModuleScript is a special kind of script that can be obtained using the require() function from any script, anywhere (as long as the script can obtain it. ex: a LocalScript cannot access ServerStorage - so it would error.)

ModuleScripts work in the same manner as normal Scripts, but functions are named slightly different. I'll show you an example:

-- ModuleScript

local module = {}
-- any functions/variables in here will be part of the module.

function module.printMyFavouriteAnimal()
    print("probiker123's favourite animal is a dog!")
end

return module

As you may notice, the function name is slightly different than what you'd expect. But it's very simple to understand. Rather than using function functionName(), instead you use function moduleName.functionName() so since "module" is the module, the function would be module.functionName().

Now that you have the ModuleScript setup, it's pretty straightforward from here. In ANY script (that, of course, can access it) you simply type, local moduleName = require(script location). This requires the module. Now to run the function from the script, you type the variable name (that you created within the server/local script) and then the function name. So here's how you'd do it.

-- Server Script
local myModule = require(game.ReplicatedStorage:WaitForChild("ModuleScript"))

myModule.printMyFavouriteAnimal()

> "probiker123's favourite animal is a dog!"

Hope this helped!