How to change the report heading based on type?

In Ar invoice report Display Credit memo for type credit memo and debit memo for debit memo type invoices.

Solution
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For this i took A form field in heading and increase size by ctrl+{ buttons or manually increase size because it is heading.

Then in  that form field write below code.

<?xdofx:if to_char(TYPE)='INV'  then ’TAX INVOICE’else if to_char(TYPE)='CM' then ’CREDIT MEMO’ else  ’DEBIT MEMO’ end if?>

The rtf Look like below...