How do I handle static data of each user without impacting others?

Static data is just that: static. There is one copy for the whole application (in a similar way to Global Variables in other languages).

If your static data contains user specific information, it will fail because it can't contain different information depending on which user is "active" within the app.

Ignore computers for a moment, and let's talk about cars.
All cars have a colour - but which colour it is depends on which specific car you are talking about. My car is black; your car is red; this car is green; that car is blue. Colour is an instance property of the Car class because you need to have a specific instance of a Car in order to ask the question "what colour is it?" - you can't say "what colour is a car?" because it's meaningless without saying which car you mean.
But cars have static properties as well: you can ask "how many wheels has a car?" because all cars have four wheels. (If it had two, it would be a motorbike, not a car!)

As soon as you start proliferating static data, the chances are your design is wrong: a well designed app will often have little or no static data at all - perhaps a connection string to a DB, maybe a URL to a website. But if you start storing information about a specific user in static data, then that is almost certainly wrong and will cause you problems.

I'd go back to your design, and work out why you think this data has to be static - and if that reason is "so this static method can access it" then you need to look at "why is this method static at all?" rather than "how can I get instance data into a static method?".
static methods should only ever work with data that is not instance related, or that can be disassociated from any specific instance and passed to the method via parameters.