Populating text in sales order based on delivery block on sales order

Hello,

We have a requirement that text in sales order header to be determined when there is delivery block at header level in sales order . that is text id to be visible in sales order header for manual entry if delivery block exists in sales order

Which user exit to be used for text to be validated against delivery block in order. If someone can answer who has worked on similar requirement ? we are not creating sales order with ref to another sales order. Someone told me RV70TNNN but not sure whether this is called when saving sales order ? If RV70TNNN is data transfer routine then we are not transferreing text from previous document.