It seems like you are looking to retrieve the entire FormArray with your getter function. In that case, all you need is this,
return this.dataForm.get('myFormArray') as FormArray;
Alternatively, if you need to access a specific control at an index within the FormArray, you can do so like this,
public getControlAtIndex(index: number): AbstractControl {
let myFormArray: FormArray = myForm.get('myFAControl') as FormArray;
return myFormArray.at(index);
}
If the control at a certain index is a FormArray, using this function to query that index will return the entire nested FormArray.
There are also other methods for retrieving the index value of a FormArray. You can find more information in this answer.
However, your approach seems a bit off. It appears that you are attempting to update the form value with what it already contains. If you want to set the initial value for each control in a FormArray, you can use something like this,
for(let i = 0; i < myFormArray.controls.length; i++) {
myFormArray.at(i).setValue(myVals[i]);
}
Or,
myFormArray.setValue(["val1", "val2", ...]);