Here is a thread from simufly that might help: http://www.simufly.com/cgi-bin/yabb2/YaBB.pl?num=1266607050

When I was learning to do this I printed this section and followed it step by step.

Check that the MI indication is 4.With MI 5 it isn't possible to perform the DME updating.

After this check you have to assign the desired DME position excluding zero.

Then right click on 7&9 to enter the DME mode.

You have at this point on the FROM-TO display FROM indicator blank and TO indicator flashing zero.

Insert the DME coordinates in the same manner you insert the waypoints.

Right click on 3&9 keys on CDU Keyboard and push N(2)to have the possibility to insert DME station elevation in thousand feet.

INSERT switch/Light push out.

Select DIST/TIME on the CDU selector and check that the DME distance on the RMI is equal at distance calculated by the INS.
WAYPT CHAN push on. Push the DME ID number and INSERT. Check that the related DME Updating flag comes green.

Exit from the DME Mode.

This procedure is sharply described on
FS9/CIVA/DOCS/OPERATIONSMANUAL chapter 5 CONDITIONAL PROCEDURES paragraph 3 DME UPDATING.
Gianfranco

I'm sure you will figure it out, Don