Hiding the "I don't know the model" option for students

I have everything set up so that Students can only see the model of laptop they are assigned when placing a ticket & when they choose it they only see specific issues for that laptop, however, if they choose the “I don’t know the model” option, it shows them all the issues for all the other laptops. These could be assigned to a teacher or central office employee and so the issues are different and I don’t want students to see those. Is there an option to hide that choice or is there another way I can accomplish this? Hopefully that makes sense!