Hey there @543764! Welcome to the community! So basically you need a couple of things. A blueprint with a reference to the Niagara system you’re adjusting. In my case I just have it as a child of the character, but you could instead instantiate it if you’d prefer and get that ref.
The from there, you’ll click float, name it something memorable. I named mine NewVal in this example.
So now let’s tie the parameter to one of the Niagara variables shall we? Click the spawn rate of your system (if that’s the float you wanna change) Then click drag the NewVal over to it like this gif. This binds the variable.
Now you’re gonna need an event, the reference to your Niagara instance, and this node.
And Voila, you have a button that can change the spawn rate of this Niagara system!