I took ishihara plate test on internet and it shows that I have red color blind (protanopia). What can cause it, and what can be done about it?

Genetics. Color vision is controlled by a gene on the x-chromosome. Females xx and males xy, making males more likely to be color blind. Of the different types, red/green is the most common, with red being a sub-type of this. You should see an ophthalmologist for an evaluation. If you are just now discovering this, it seems like you are pretty well adapted to your situation.