Hi today i completed the quest and choose wrong weapon i wanted greatsword and accidentally take dagger can i switch that somehow ????
Collect all 5 forms of Caladbolg. There are two ways to do this (one easy, one expensive):
After completing the Knight of the Thorn achievement, you can return to your Home instance where Ridhais will be waiting. For 1000 Unbound Magic, she will allow you to trade in your current Caladbolg and let you choose another form. Doing this four times, once for each form, will give you the achievement since you just need to unlock each skin. You will only have 1 weapon at the end, though.
c and p from the wiki