I'd like to mention a couple of details about converting date values from Excel into dates in R. The origin argument of as.Date designates the date that has the value 0. That is 1899-12-31 in Excel. However, Excel also accepts 1900-02-29 as a valid date though 1900 was not actually a leap year. For date values after 1900-02-28, you have to use 1899-12-30 as the origin in as.Date to get the correct date in R. A date value of 43913 represents March 23, 2020 in Excel.
as.Date(43913,origin="1899-12-30")
[1] "2020-03-23"
If you need to convert characters to dates, you can use code like
DF$Date <- as.Date(DF$Date, format = "%d/%m/%Y")
where the format argument shows the format of the imported characters, not the format of function output. The lubridate package has handy function for converting characters to dates. If the characters are in Day-Month-Year format
DF$Date <- lubridate::dmy(DF$Date)