Exclude value in the list when the value already occur in Appsheet

[ac111]

Dear All, 

I would like to ask, since I am still newbie in Appsheet. 

How can I remove/exclude in the list name dropdown, when its already appear the name in another field. May refer diagram below for more understanding.

I would like in my 'Siblings dropdown list' only can see those 3 names only (Agnes Monica, Ronaldo and James)

Seek your help. Thank you.

[Steve]

Look here: Subtract values from a list