What to do if I had a blood test my red blood cell is 4.83 and platelet count 421 is that dangerous?

Not dangerous. Your platelet count is slightly high, normal count being 150-350, 000. Red blood is best measured with hemoglobin level. Although your platelet count right now is of no serious medical concern , it may be worth rechecking it once more in one month and see if it drops below 400, 000. Anything over 450, 000 would need further attention and medical examination by a hematologist.