I've got python 3.6 in this directory:
How can I set in .emacs path to python 3.6 interpreter?
(setq exec-path (append exec-path '("d:/Python36/")))
python-shell-interpreter is the variable you are looking for. You can set it using
(setq python-shell-interpreter "D:\Python36")
Add this to your
.emacs and reload python process.