2.0 relic meld help

i am currently melding materia to my 2.0 relic. FYI i am getting it for glamour purposes. I have it for a blm but when i check my weapon i dont see any meld option why

There's lots of reasons...
do you have the right materia grade?
do you have Alexandrite?

That's because you don't meld it directly onto the weapon. You should have been given a scroll that you meld materia onto using alexandrites instead of carbonized matter. Once you've done all 75 melds you'll take it back to Jalzahn to apply the scroll w/ melded materia to your weapon.