Hi @Smitha,
Welcome to the RStudio Community Forum.
Your code line probably needs to be edited to the following:
write.csv(dat_sites_final, file=file_save, row.names=FALSE)
Note that R is case-sensistive and doesn't like stray spaces in function names.
This should work as long as "dat_sites_final" and "file_save" contain the correct content.
Try help(write.csv) for more information.
HTH