State tax filing

You are confused because of the word "tax"   ... the HOMESTEAD tax credit  reduces your REAL ESTATE taxes  it is NOT an INCOME tax credit on the state income tax  return thus there is no place to enter it.   

You file the application to have a homestead exemption put on the property so you pay less RE taxes  not less income taxes   ...  https://tax.iowa.gov/sites/default/files/2020-01/HomesteadTaxCredit%2854028%29.pdf