The refining will be done by God
People have to change themselves, though.
Yes, God provides the means to refine them, but they have to take the appropriate action, to clean themselves, by repentance and obedience.
That has always been the case, as we read throughout the Scriptures. Romans 12:1-3 is one such passage.
I am thinking that the JWs have written their own bible molded to their own viewpoint.
No. As with all other verses that are deemed questionable by some, the following versions put that accusation to rest, at least here in regard to Daniel 12:10; they read similar to NWT:
English Standard Version
Many shall purify themselves and make themselves white and be refined, but the wicked shall act wickedly. And none of the wicked shall understand, but those who are wise shall understand.
JPS Tanakh 1917
Many shall purify themselves, and make themselves white, and be refined; but the wicked shall do wickedly; and none of the wicked shall understand; but they that are wise shall understand.
American Standard Version
Many shall purify themselves, and make themselves white, and be refined; but the wicked shall do wickedly; and none of the wicked shall understand; but they that are wise shall understand.
English Revised Version
Many shall purify themselves; and make themselves white, and be refined; but the wicked shall do wickedly; and none of the wicked shall understand: but they that be wise shall understand.
World English Bible
Many shall purify themselves, and make themselves white, and be refined; but the wicked shall do wickedly; and none of the wicked shall understand; but those who are wise shall understand.
Young's Literal Translation
Purify themselves, yea, make themselves white, yea, refined are many: and the wicked have done wickedly, and none of the wicked understand, and those acting wisely do understand;