When using the labeler in V2, it's a good idea to stop the server or at least
make sure there won't be any migration, reclamation or restore processing
going on.

Then -

c:\win32app\ibm\adsm\utils>dsmlabel -drive=mtx.0.0.x,elementnumber 
-library=lbx.0.0.x -overwrite

where the x's are the numbers for your specific configuration (you can see
these from the utilities interface - diagnostics screen.  You also need
to know the element number of the drive you are using.

Don't use -search, -keep or -barcode.  You will be prompted to put the
tape in the slot and then to respond with the label number.  Do this 20 times.