You will want to clone the repo and run the packer install. It may require a little tweaking if using on windows as I store a fair bit in ~/.local on macos/linux and my home directory is initialised by the setup scripts not the neovim scripts.
When I want to reset my local install I run the following which can probably be adapted for Windows:
rm -rf ~/.local/share/nvim && rm -rf ~/.cache/nvim && git clone --depth 1 https://github.com/wbthomason/packer.nvim ~/.local/share/nvim/site/pack/packer/start/packer.nvim
I'll write this up later. Maybe.