Adjust date format after using dput in R - r

Question

As you can see, it misconfigured the date in my database. How can I fix this or is it that way??
library(readxl)
df<-read_excel('C:/Desktop/example.xlsx')
dput(df)
> dput(df)
structure(list(Date = structure(c(1629936000, 1629936000, 1629936000,
1629936000, 1629936000, 1629936000), class = c("POSIXct", "POSIXt"
), tzone = "UTC"), Upd = structure(c(1577836800, 1577836800,
1577836800, 1577836800, 1580601600, 1580601600), class = c("POSIXct",
"POSIXt"), tzone = "UTC"), `Value 1` = c(12, 12, 3, 4, 5, 6)), row.names = c(NA,
-6L), class = c("tbl_df", "tbl", "data.frame"))

Answer 1

You could reformat the data:
library(dplyr)
df %>%
mutate(across(c(Date, Upd), ~format(.x, "%d/%m/%Y")))
This returns
# A tibble: 6 x 3
Date Upd `Value 1`
<chr> <chr> <dbl>
1 26/08/2021 01/01/2020 12
2 26/08/2021 01/01/2020 12
3 26/08/2021 01/01/2020 3
4 26/08/2021 01/01/2020 4
5 26/08/2021 02/02/2020 5
6 26/08/2021 02/02/2020 6
Or with base R
df$Date <- format(df$Date, "%d/%m/%Y")
df$Upd <- format(df$Upd, "%d/%m/%Y")

Answer 2

In base R
df[c("Date", "Upd")] <- lapply(df[c("Date", "Upd")], format, "%d/%m/%Y")
-output
df
# A tibble: 6 x 3
Date Upd `Value 1`
<chr> <chr> <dbl>
1 26/08/2021 01/01/2020 12
2 26/08/2021 01/01/2020 12
3 26/08/2021 01/01/2020 3
4 26/08/2021 01/01/2020 4
5 26/08/2021 02/02/2020 5
6 26/08/2021 02/02/2020 6

Answer 3

I'm not sure if this is exactly what you're going after, but I deal a lot with excel files where a column that should be a date get's imported as numeric. I made this little function to help me out with that:
excel_date_number_to_date <- function(number) {
as.Date(number, origin = "1899-12-30")
}
For your dataframe you can use it like this:
df %>%
mutate(across(c(Date, Upd), ~excel_date_number_to_date(.x)))