Edit any purchase line below — product name, HSN, GST %, quantity, unit, rate, or supplier info — then click Save on that row. Saving always recomputes taxable value/CGST/SGST/IGST/total from quantity × rate, and rolls the parent invoice's totals up too if this line belongs to one. This does not adjust stock or FIFO batches — a purchase's quantity here is the total across every panchayath its stock was split into, so there's no single place to safely apply the correction. For a stock fix use Adjust Stock on the product's edit page, or void this purchase (in Purchase Register) and re-log it if the stock impact itself needs to change.
Tip: filter by Bill No or Token No above to pull up just the lines from a bill you forgot to add a supplier to, then check the rows and apply one supplier to all of them. Individual rows can still be edited/overridden below afterwards.