According to 1 Kings 8:9, there was nothing in the ark but two stone tablets.

There was nothing in the ark except the two tablets of stone that Moses put there at Horeb, where the LORD made a covenant with the people of Israel, when they came out of the land of Egypt.

Hebrews 9:3-4 says it also had Aaron's rod and a pot of manna in it, but that is probably conflating some verses from Exodus 16:33-34 and Numbers 17:10 which say that those other items were in the Holy of Holies, but not specifically in the ark.

There is nothing in the Bible saying anything else was in the ark and nothing about seven books being associated with Solomon or Solomon "changing his mind about religion or evolution." Solomon is depicted as faithful from childhood and actually starts to slip into idolatry after marrying foreign wives. 1 Kings 3 says Solomon was given his wisdom after praying to God and asking him for it.

I'm unaware of and cannot find anything even in apocryphal traditions or writings about anything else being in the ark or seven books being associated with Solomon in any manner. Solomon is traditionally the author of some of the books in the Bible (Song of Solomon, Proverbs, Ecclesiastes), but not seven of them. Your friend might possibly be remembering something about Josiah and the discovery of the "Book of the Law" in the Temple in 2 Kings 22. In that story, the discovery of a scroll allegedly written by Moses causes Josiah to rend his clothes and to institute a series of reforms, but that was Josiah, not Solomon, and it was only one book.

There is nothing anywhere in the Bible or any other writing from antiquity about evolution.