first of all.....improvement exams will be conducted next year for those students who have appeared this year for 12th exam and feel like they can perform better if given one more chance. As exam will be next year you need not to worry now, about forms ....wait till the results.In August or september..just visit regional office of (In your area).Ask them for form for improvement,it is free of cost.Fill the form,you will require to submit fee for appearing in papers through demand draft(dd).submit your form there at cbse office and you are done.Wait till march when you will receive your admit card along with name of your centre ....give exam there with other regular board students ..and thats it...If you have further queries,ask me for my contact number.Happy to help…...please ignore grammatical mistake....good luck