Just got the last sword fragment last night. Make that about a week to get all fragments, unless you are luckier.
Step 1: Must have all 3/3 fragments.
Step 2: Mix and you will get the sword reforged.
Step 3: Close and equip Jarvis with the sword.
Now that he is all equipped, he could now be promoted.
More powerful, more intelligent, more agile and great and commanding. This will increase percentage of infantry, cavalry and magic attacks and defenses.
You could see that my dashing Jarvis is now +1 (Common) and has new promotion ahead of him and then he may unlock other skills.