Assuming that the question is how to convert the input x shown below to Date class use as.Date with a format that corresponds to the input so it must start with X, have dots where the input has dots, etc. Look at ?strptime for documentation on the percent codes.
x <- c("X1.22.20", "X1.23.20") # input
as.Date(x, format = "X%m.%d.%y")
## [1] "2020-01-22" "2020-01-23"
Note that if you got those dates like this:
Lines <- "1.22.20 1.23.20
1 2
3 4"
read.table(text = Lines, header = TRUE)
## X1.22.20 X1.23.20
## 1 1 2
## 2 3 4
then the X can be avoided using check.names = FALSE as follows:
read.table(text = Lines, header = TRUE, check.names = FALSE)
## 1.22.20 1.23.20
## 1 1 2
## 2 3 4