I had this problem too one time, we had the Evenflo Triumph 5 (our's was manufactured in Aug. 2004). I am not sure of the differences between the 5 and the LX, but the tether is probably the same because we had the same issue.
It did not say anywhere in our manual either of how to put the tether back on. We had to look at every picture in the manual and really try to see what the tether looked like (how it was looped) and play around with it.
We did figure it out after some fiddeling, but I don't have the carseat anymore now (sold) so I can't tell you how to do it for sure.
Sorry I am no help but I just wanted to say this was very frustrating for us to figure out. Try to look closely at the pictures and play around with it. You should also call Evenflo and ask them if they can help.
Anyone here have a Triumph that they can look at???
Edited to say that you should probably also post this question in the "Car Seats" forum. I have seen a ton of questions about car seats there and everyone is always really helpful. Here is the link..
http://www.car-seat.org/forumdisplay.php?f=2