Vo2Max not change even after many run

Hi ,

I'm new on garmin (before fitbit) For a month, I have a new forerunner 245. my vo2max score is very bad (32) and whose move.

I run 30km by week. he seems to ignore my activities. if i compare to fitbit my vo2max score was above 50. do you have any idea why my vo2max score does not move on garmin

thank you for  help.