How do i assign my credit customers as Trade debtors ?
Your question is not clear. A debtor is someone who owes money. In that sense, a customer already is a debtor, because they owe you money.
How do i assign a customer as Trade debtor in summary report ?
What do you mean by “trade debtor?” And which summary report? If you are vague with your questions, other forum members cannot help you.
under income, i would like to see trade debtors as outstanding balances.
how do i assign my customers under trade debtor group or account ?
Outstanding balances are not income. If you are referring to showing how much customers owe you, such amounts would appear in asset accounts. By default, customer balances owed show up in Accounts receivable. But if you want, you can assign customers to custom control accounts. See https://www.manager.io/guides/9256.