You are trying to use dplyr's select; however it appears that you have loaded another package that also defines a select function after loading dplyr and thus masking the one from dplyr.
Restart your R session, and load all the packages you use, while keeping an eye out for messages. 
Try specifying the namescope by calling 
Attrition_edufield <- myds %>%
  dplyr::select(Attrition, EducationField) %>%  # that's dplyr with two colons in front
  group_by(Attrition, EducationField) %>%
  summarize(count = n())
As an alternative, check that your variable myds is a data.frame (or related structure) and contains the columns you are trying to select.