[SQL] SQL conversion help

Hello,

I have below SQL script used in SQL Server. I would like some help to
convert it into PostgreSQL format, please.

DECLARE @satirno INT
SET @satirno = 0
UPDATE urtrecetedet
SET @satirno = satirno = @satirno + 1
WHERE recetekodu = 'ASD'

Thanks & regards,
Ertan Küçükoğlu