I used to update the material file at my last 2 jobs.
Solidworks has there standard material file (.sldmat)
I would suggest looking for it and saving it as a different name.
Then you can open it up in Notepad and make sure you study
it first to know where one material starts and finishes as well as
where the categories start and finish.
Then if you have all of the properties i.e. density, poisons ratios, tensile strength etc.
then copy an existing material place it properly and change its description. I would suggest
changing all of the specs in Solidworks and applying it to this new matieral file.
Make sure this new material file is in a network location and pathed correctly using the system
options>file locations>material file.
One other thing is there is a website called Matweb that if you have a subscription you can
down load your material specs directly into a Solidworks format.
I hope this makes sense to you. I know it can be confusing.