@divegeester
Maybe I misunderstand your question.
What I read is:
How can you not know that “precious blood” in in the Bible?
The typo "in in" I assume means "is in".
Then if that correction is valid then I read
How can you not know that “precious blood” [ IS ] in the Bible?
You can know that phrase
"the precious blood of Christ" is mentioned in the Bible by reading the Bible.
You can know that that blood of Christ is precious at any point along the way of your reading the Bible given that you believe it applies to you.
You can know that that blood is precious in its application to you by you confessing your sins and experiencing your conscience put at perfect peace by God's forgiveness.
You can also come to a realization its preciousness by being shepherded and helped by a more experience believer who teaches you something of applying the blood of Christ specifically to your confessed sins.
It is precious because redemption is precious.
It is precious because God's forgiveness is precious.
It is precious because the peace that only God can give a human spirit and
heart is precious.
You mix the word of God with faith. And it becomes a precious truth that you taste subjectively and not just read objectively and academically on a page in black and white.
When we come to the Scriptures we should also simultaneously come to God.
When we come to the word of God we should come with an attitude willing to be changed by God, reaching out to God, trusting in God, turning our heart to God.