There are no charges to convert an intraday order to a delivery order.
To convert an intraday order to a delivery order, you need to have sufficient funds in your trading account to accommodate 100% of the trade value as upfront margin in case of a buy trade. If the open intraday position is a sell transaction, you need to have the required holdings in your Demat account for the said stock.
You need to pay brokerage charges and other regulatory charges as applicable for a CNC order.