Formarray PatchValue в индексе
patchDynamicFormBlockValue(){
this.alternateEmail.at(<index>).patchValue('patchmail@gmail.com')
}
Vast Vicuña
patchDynamicFormBlockValue(){
this.alternateEmail.at(<index>).patchValue('patchmail@gmail.com')
}
((this.form.get('controls') as FormArray).at(index) as FormGroup).get('description').patchValue(item.description);