did you get an error ?
it would be rational to quote the error you receive... but in this case I can predict what it would be.
it could be that you havent loaded the assumed tidyverse library , which includes the tidyr library of which separate is a function.
even then, tidyr::separate does not process raw character strings, it processes dataframes with character columns.
Here is a complete example
library(tidyverse)
(x <- c("33.54+72.97","33.56+72.91"))
(my_x_df <- enframe(x))
separate(my_x_df,col=value,
into = c("LAT", "LONG"),
sep = "\\+" )