Thanks for asking a question on www.thisisyourbible.com
The passage to which you are referring is Revelation 13:8
Revelation 13:8 And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world.
This is as ambiguous in the English translation as it is in the Greek original - ‘from the foundation of the world’ can be read as applying to ‘the lamb slain’ or ‘not written in the book of life’.
It is better understood if we read it as:
‘whose names are not written, from the foundation of the world, in the book of life of the Lamb slain’.
That this is the correct way to understand it is confirmed in Revelation 17:8.
Revelation 17:8... and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.
Christ’s death was foreordained (foreknown) before the foundation of the world, but it is certain that he only died once in approximately AD 30.
Hebrews 9:26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.
1 Peter 1:20 Who verily was foreordained before the foundation of the world, but was manifest in these last times for you,
I hope you have found this helpful.
God bless you,