Hi @apkoh18 :
Could you please tell me:
1\Is PersonColumn a person type column which allow multiple selections? I assume it do not allow multiple selections.
2\What is Person( in PeopleList) 's date type? I assume it is a text column.
3\What is the dropdown you mentioned?Is it a combo box control or a dropdown control?I assume it is a combo box control.

4\Does the Person column in PeopleList store the user's DisplayName?
5\What is the dropdown/combo box's items property?I assume it is
PeopleList
6\Do you want to set the dropdown/combo box's default items to be the person which is selected by ValueCard_DataCardValue? If so please set the combo box's DefaultSelectedItems property to:
LookUp(
PeopleList,
Person=LookUp(
'SoureList',
ID= Value(ValueCard_DataCardValue.Selected.Id),'PersonColumn'
).DisplayName
)
Best Regards,
Bof