You won't be able to delete... [ POST EDIT Sorry - yes you can. I'm too used to being on the12volt! ]
But that shouldn't matter - unless I have misunderstood OP Champak or camo.b's replies, this is a question of signal conversion, not power conversion and most readers should be aware of that. (Else if someone could please tell me how I misinterpreted?)
A dc-dc converter would not be used to provide the signal power for a relay. Besides, there is no info about what power the output can provide.
But IMO the solution has been given. More questions or detail is needed for before more is posted or bantered by us. Then we can decide if alternatives are needed (like an OpAmp or Comparator circuit etc).