When can I ask for retrial before sentencing or after this is for criminal matter
In CA it's called a motion for a new trial and you must do it before sentencing. See CA Penal Code § 1181.
You need to file it before sentencing.
Criminal Defense Attorney
You must file a motion for a new trial prior to sentencing.
Federal Crime Lawyer
The answer depends on whether this is a state or federal case. In a state case, the motion for new trial must be brought before sentencing. In Federal Court, you have only 7 days to file the motion for new trial from the date of the verdict or guilty plea unless within that same 7 days the court grants an extension. The only exception to this is when the motion for new trial is based on newly discovered evidence. That is the only exception to the 7 day rule. A motion for new trial based on newly discovered evidence has a 3 year limit.
The 7 day limitation is jurisdictional--this means the Court no longer has authority to consider a motion after the 7 days. The federal rule is very harsh.