I’m getting confused by scriptures that say “and they called upon the Lord“ when prayers are supposed to begin “ Dear Heavenly Father.”
I’m interpreting your question to mean that “the Lord” refers to the Son, not the Father. That is not always true.
Let’s take a look at they etymology. “Lord” means ruler, master, superior, or God. It comes from the ancient meaning of “guardian.” There was such a marriage of the concepts of rulers and guardians, that it was naturally understood that the rulers were responsible for the safety and security of those under their rule.
In previous centuries, this title was what we applied to those whom we call managers and bosses today. At the office, you may have several people that you call “boss.” A manager, assistant manager, office manager, Company President, CEO. They’re all your ‘boss”. But only context will tell you which one is the one you are really referring to.
“Lord” simply means “a ruling authority.” Proper context is required to determine which one is being referred to. In gospel settings, sometimes this refers to the Father; sometimes, the Son, others, the Godhead as a whole, or even a generic term for Divinity.
We do call upon the Lord in prayer. And this means that we call upon the Father in prayer, in the name of Son, by the power of the Holy Ghost.