Continuing the discussion from How to access Rename Tool from backend?:
Anyone to explain how to use this feature, please. Thanks
Hi @Peter_Macharia :
Use bench bulk-rename YOURDOCTYPE PATH where
YOURDOCTYPE: Your doctype 
PATH: A CSV file with data (, this way
|OLDITEM1|NEWITEM1|FALSE|
|OLDITEM2|NEWITEM2|FALSE|
…
|OLDITEM10|NEWITEM10|FALSE|
3th column is used for merge (combine with existent one)
Hope this helps.