You mean amend it back to its original intent?
Very easy! We don't have to change a word. We simply ratify a new Establishment Clause modeled word-for-word after the existing version.
And if that's the case, why are we amending it at all?
I cannot believe the depth and breadth of stupidity and ignorance on the history of this particular issue. It is absolutely mind-boggling.
James Madison, principal drafter of the First Amendment, thought that it prohibited Congress from hiring chaplains, and the President from proclaiming Thanksgiving Day. His thoughts on the subject are here.