Copy calculated column to another column in same list

I have a list with the columns rID, requestID and some other columns. Here rID column is type number and it will set the value from workflow. requestID is type calculated column and starts with some text like =""&"REQ_"&rID

Now I want to show this requestID in dispForm.aspx (view item). It's a calculated column so any suggestions to display in view item?

Or how do we copy this calculated column value to other column type string in the same list?