cljfmt is included with both Clojure-LSP and CIDER, so if you have either installed it should work out of the box.
With LSP mode the standard `lsp-format-region` and `lsp-format-buffer` commands should work, and on the CIDER side `cider-format-defun`, `cider-format-region` and `cider-format-buffer` should also invoke cljfmt.
I'll add a note to the cljfmt README to tell people about these commands, as your experience shows that it might not be obvious to people that they likely already have access to cljfmt in Emacs as a result of using LSP or CIDER.
With LSP mode the standard `lsp-format-region` and `lsp-format-buffer` commands should work, and on the CIDER side `cider-format-defun`, `cider-format-region` and `cider-format-buffer` should also invoke cljfmt.