You can call External r markdown page from r script using render function.
Syntax: rmarkdown::render(rmd_file, output_type, output_file_name, knit options,....)
Suppose you have a Rmd called test1.Rmd.
To call the Rmd file use R code as
rmarkdown::render("test1.Rmd")
#You can also specify the type of output file and pass parameters using render() to actual Rmd file to display output.