Hi @Anonymous,
I will share a short explanation about the form control.
A Form control is used to display or edit/Update record from a Table (Data Source), with Data Source property set to table, and item property set to the proper record.
For Each field(Column) in the table, there would be a corresponding DataCard generated, which is used to show the column name and the related value.
Specially, for EditForm, for each DataCard, there would be an Update property, which is used to Update the value of the related fields.
Read more here:
Understand data forms in Microsoft PowerApps
In addition to adding the dropdown control, you would also need to modify the Update property of the corresponding DataCard,
For example, if here you would like to update the field with the Dropdown selected value, then we should modify the update property of the DataCard to:
Dropdown.selected.value
For more information about DataCard, check:
Understand data cards
Regards,
Michael