how to add vendor bank details on saved transaction search on bill

I dont think you can Check if you have on your transaction search : vendor…bank details But probably you can with analytics dataset

bank details are a sublist from vendor record so you need to pull them to e.g. vendor record first, analytics I think can do it - but note that it can be one to many - so you should settle on some criteria, like only primary or whatever setup you have

otherwise you can create a source field dynamically on the supplier file which will show the bank details then a wf which copies field not stored to a stored field