Select the character you want out of your party from the Characters Nearby and pick the Ask action. You should see an option such as "We should part ways..." or something like that.
19 days ago(+1)
Ooh yeah this is a special case because you're in the middle of a quest with Ebiko. I recommend you continue Ebiko's quest until she leaves your party. Then you can do the other quest you're trying to do.