Suggestion:
The System does not allow to cancel the Sales return and change the supplier name in Purchase return.
Users will have to follow the below procedure to do the corrections in the Purchase return of the correct supplier and Sales return on A site.
1. Once the Purchase return is done from wrong supplier site C.
2. Do the dispatch and Invoice from site A will decrease the stock from site A location .
3. Purchase receipt will generate on site B with the correct supplier , which will increase the stock on site B location .
4. Do the Purchase return on Site B for correct supplier and Sales return on A site.