Hi @bbsin,
I have mentioned the details in my previous reply, hope you could check it and try again.
You make me confused, you said that you want to remove the data card and replace it with the Checkbox, however you keep the TextInput and want to display something in TextInput based on checkbox value, which drive me dizzy.
I will repeat my solution one more time.
1). Select the Declare(C)DC and DELETE it from the data card
2). Since the field is text type, set the Default property of Checkbox:
If(ThisItem.ApplicantInfoDeclare= "Yes", true, false)
3). Set the DataCard's Update property to:
If(Checkbox.Value, "Yes", "No")
4). REPLACE the Checkbox with the real checkbox name in your scenario.