Full transparency: This is likely not the most efficient way of doing this, so if an expert shows you a different way, please use their technique. However, this code does get the job done.
You only need to run this once
install.packages(c("readxl", "stm", "textclean", "tidytext", "tm",
"tokenizers"))
Here are the packages you need to run topic modelling and what they do
library(readxl) # read in your excel file with text in it
library(stm)
library(textclean)
library(tidytext)
library(tm)
library(tokenizers)