I have a csv file with time as the datetime format and want to edit the same column into miliseconds, how do I change that?
Familiarize yourself with the pandas library, which allows you to do this:

from pandas import read_csv
from io import StringIO
csv_file = StringIO("""time event earthAcceleration.x earthAcceleration.y earthAcceleration.z
2017-11-22T09:20:13.944 motion -0.006379993 -0.001029071 -0.010781396
2017-11-22T09:20:13.954 motion 0.014739769 0.008146121 -0.001068155
2017-11-22T09:20:13.964 motion 0.008520941 -0.008222823 0.022573506
2017-11-22T09:20:13.974 motion 0.000573836 0.016701656 -0.016170829
2017-11-22T09:20:13.984 motion 0.016282924 0.003181049 0.006969224""")
df = read_csv(csv_file, sep=' ', parse_dates=['time'])
df.assign(delta_t = df.time-df.time.ix[0])


I believe your output is wrong; the difference between each line is exactly 0.01s. Welcome to the site!