
When run mutate like you do, it worked!
Thanks for all !!!!!
I will change my class data from dataframe to Tibble.
With this code:
for (i in 1:nrow(data01)){
data01[i, 2] <- mdy(str_remove_all(str_to_lower(data01[i, 2]), ","))
data01[i, 4] <- mdy(str_remove_all(str_to_lower(data01[i, 4]), ","))
}
Result:

With your code:
datay <- data01 %>% mutate(exdividend_date = mdy(str_remove_all(str_to_lower(data01[i, 2]), ","))) %>%
mutate(payment_date = mdy(str_remove_all(str_to_lower(data01[i, 4]), ",")))
Result:

I'm sorry because I don't know how to use dput(). I tried, but I didn't get it. 