Open Your Blogger Account , Then click on layout section, see image for reference. Now you will see lots of Add a Gadget button. Choose one of them wherever u want to add contact form . Click on it and you will see contact form, choose it and save.
Go to blogger.com or https://draft.blogger.com . Open the published post or new post if you want to edit cutom permalink of already published post and see the referene image below !