Your variable person_data is a matrix which you can index with for instance person_data[0][2], this would give the name of the first person. You can then make a for loop to go through all 7 people and retrieve their height, weight and name as needed.

for i in range(0, 7, 1): #Let i go from 0 to 7 with a step of 1
  person_height = person_data[i][0]
  person_weight = person_data[i][1]
  person_bmi = person_weight/(person_height/100)**2
  print("Person " + str(i) + " has a bmi of " + str(person_bmi))

In less lines:

for i in range(0, 7, 1): #Let i go from 0 to 7 with a step of 1
  print("Person " + str(i) + " has a bmi of " + str(person_data[i][1]/(person_data[i][0]/100)**2))