How do I create function to generate plot for each column

here is an example dataset:

Group<-c("Blue","Red","Green","Blue","Red","Green")
UV<-c("3","4","2","5","4","6")
Rain<-c("10","11","12","15","16","17")

dmean<-data.frame(Day,Group,UV,Rain)

Day<-c("1","1","1","1","1","1","2","2","2","2","2","2",)
Group<-c("Blue","Blue","Red","Red","Green","Green","Blue","Blue","Red","Red","Green","Green")
UV<-c("3","3.1","4","4.1","2","2.2","5","5.1","4","4.2","6.1","6.1")
Rain<-c("10","10.1","11","11","12","12.2","15","15.2","16","16.1","17","17.2")

dpoints<-data.frame(Day,Group,UV,Rain)

Basically, I have a large dataset with multiple variables, in this example here,"UV" and "Rain" which I group by "Day" and "Group". I want to generate a plot for each column, eg "UV" and "Rain" using geom line to connect the mean values from "dmean", together with the data points in "dpoints" using a function as below which may not be right and incomplete:

plot.ts <- function(d){
  
  ggplot(dmean, aes(x = Day, y = col.num+2, group = Group, colour = Group)) +
    geom_line(size = 1)+
    geom_point(dpoints, aes(y = d0[,col.num+2]),
               alpha = .2) +
    facet_wrap(~Group, 
               ncol = 1) +
    ggsave(paste0("plot1_",col.num,".png"), width = 15, height = 10, dpi = 300, units = "in", device='png')
  
}

Here is an example figure for "UV" which I hope to generate along with other variables too. Could someone please check through the function and apply the function through the columns?