Not quite sure what you mean...but have you tried making a new Layer "Rain" Put your Rain Fx/object in that Layer, then set the Layers Parallax & scale rates to 0 in the Properties pane for the Layer..
This will make that layer always be fixed on whatever is being "scrolled to" Hopefully your player,
It will appear to rain over the area that is currently viewed..
There of course are plenty of other ways to do it..such as Pinning your Rain Object to the Player or setting its X,Y pos to the players Every tick
Any of those should do it..
personally I would use the Layer technique as it sometimes you make want a Cinematic camera pan and its nice if the rain follows the view..
When in doubt..or you are lost in a Zombie apocalypse or someone is giving you a hard time..Remember one thing..... Read the Construct 2 Manual..it will save your life.:)