Help setting up DKIM for mail for a domain

I need someone to prepare a document with step by step instructions showing how to create the DKIM for a mail server. This is a ubuntu 20.04 LTS mail server with postfix and dovecot. You will explain how to generate the private and public key on the server and where to place them, and then explain what to modify in postfix etc. to make it work. Next you will explain what to add to Cloudflare to make it all work well. If you need a server to test on, I will provide a virtual server with domains for testing. Once you provide the instructions, I will follow them on my own to install the DKIM on our mail server. If it works, you get paid. This is very easy for someone who manages mail servers and should not take more than a few hours so don't bid for 7 days.