Hello @Ramesh Veera ,
You could configure a new Result source in the origin site collection (SC A in your case) and make it pull results from the destination Site Collection (SC B).
To know more about result source please refer this.
I created a new Search Result Source with a below query text.
**Site Settings (site_url/_layouts/15/settings.aspx) -> Site Collection Administration -> Search Result Source -> New Result Source **
I gave a name and clicked on the Launch Query Builder to build a custom Query Text.
You could refer this to know more about building queries and you could customize further as per your needs
Now save this Result source and make this as Default Result Source for the site collection
The above query pulls all items from the SearchBox which contains the Path of the other site collection. Now when you perform search you will get results from path defined in the custom Result source
Hope this Helps :)