You get knots out by working them. I pick, knitting needle or similar (eg marlin spike) will all do.
The good news for you is that Amsteel is very tough, so it is not easy to damage the fiber while taking apart a knot. Yes, you are right that it is highly recommended that you splice rather knot Amsteel rope, but it does not suffer the weakness of of a kind of predecessor, kevlar, which was substantially weakened by small radius knots even after the knots were undone.
If any of the above is wrong, a google search should turn up the error(s)