Recover previous value of R environment variable "PATH"

Question

I have R 4.1.2 with RStudio 2021.09.2 on Windows 10 Enterprise on a University network. When I installed Rtools 4.0, I followed forum advice for putting Rtools on the path, including the following console commands:

write('PATH="${RTOOLS40_HOME}\\usr\\bin;${PATH}"', file = "~/.Renviron", append = TRUE)
Sys.setenv(PATH = paste("C:/Rtools/bin", Sys.getenv("PATH"), sep=";"))
Sys.setenv(BINPREF = "C:/Rtools/mingw_$(WIN)/bin/")

This has overwritten "PATH" and now R is unable to open system libraries. When I start RStudio I now get this error message:

During startup - Warning message:
package ‘stats’ in options("defaultPackages") was not found 
Error in inDL(x, as.logical(local), as.logical(now), ...) : 
  unable to load shared object 'C:/Program Files/R/R-4.1.2/library/stats/libs/x64/stats.dll':
  LoadLibrary failure:  The specified module could not be found.

Instead of appending the Rtools PATH, I seem to have deleted the previous value of PATH:

> Sys.getenv("PATH")
[1] "C:\\rtools40\\usr\\bin;"

I tried accessing .Renviron using usethis::edit_r_environ but this package no longer works now.

> usethis::edit_r_environ()
Error in inDL(x, as.logical(local), as.logical(now), ...) : 
  unable to load shared object 'C:/Program Files/R/R-4.1.2/library/stats/libs/x64/stats.dll':
  LoadLibrary failure:  The specified module could not be found.

I would like to recover the previous value of PATH but I don't know how to find out what this was. How can I do this? I'd rather not delete and reinstall R unless absolutely necessary, as this is on a University system and I don't have admin rights.

Edit: Now fixed! Using R itself (instead of RStudio) I was able to access .Renviron using usethis::edit_r_environ() and delete the entry PATH=...

Then after restarting R, PATH reverted to its original value.