So there is no file named Prod.xls in your working directory. You see which directory is the current working directory with the command
getwd()
You can see the files in that directory with
dir()
If the file you want is in the current working directory, you probably have a typo in the name. Might it be Prod.xlsx? If the file you want is not in the current working directory, you can load it by including the directory path in the read_excel() function. For example, to load a file named Prod.xlsx that is on my desktop, I would run
readxl::read_excel("C:/Users/fjcc/Desktop/Prod.xlsx")
That is a Windows path. On Linux or MacOS, it would look quite different.
The fact that running readxl::read_excel() does not throw the "could not find function" error but running plain read_excel() does throw the error shows that you did not load the readxl package successfully with library(readxl). Was there any error message when you ran that?