If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.
Otherwise, we can only give you general examples like this one
library(dplyr)
library(lubridate)
# Made up sample data (replace this with your actual data frame)
Activity2015_2017 <- data.frame(
ActivityDate = factor(c("01Apr2015", "01Apr2015", "02Apr2015", "03Apr2015"))
)
Activity2015_2017 %>%
mutate(ActivityDate = dmy(ActivityDate))
#> ActivityDate
#> 1 2015-04-01
#> 2 2015-04-01
#> 3 2015-04-02
#> 4 2015-04-03
Created on 2020-11-22 by the reprex package (v0.3.0.9001)