@chegab1 - you cannot submit data from a Custom Card. The Data Cards supplied to your Edit Form are bound to existing fields in your data source.
A Custom Card added to a Form is used generally for display purposes or to perform some other function you might need in your App. You will notice for example that a Custom Card does not include an Update property.
1. Assuming the field you want to save in datasourceA is a Single Line Text data type, add the DataCard for that field into your Edit Form control.
2. Unlock the DataCard
3. Insert a Dropdown control into that DataCard
4. Delete the default TextInput control inside the DataCard
5. Address the Y property error by replacing the deleted control with the name of your Dropdown control
6. Update the Items property of your Dropdown control to return datasourceB
7. Update the Default property of your Dropdown control to either:
ThisItem.'Your Single Line Text Field'
Or:
Parent.Default
8. Correct the Update property to:
Dropdown1.Selected.'The field you want from datasourceB'
