BAD DEBTS TREATMENT IN GST

Please help me

Mr. A sales goods to Mr. B and mr. A filed their GSTR 1 gst paid in same month in GSTR 3B

but Mr . B not paid amount to Mr. A within 180 days or onward

In this case Mr. A want to recover gst output tax paid

How Mr. A recover output tax paid in GSTR 3B