I would change the value of offset = 8 and the value of actionButton arguement width = "130px".
I often find useful Shiny HTML tags like line break br(), using it above actionButton column turns aligment a bit smoother.
You may ignore actionButton's arguments icon and class if you don't like Bootsrap customization.
Does this look better?
fluidRow(
column(width = 6, offset = 8,
# width The grid width of the column (must be between 1 and 12(max.))
# offset The number of columns to offset this column from the end of the previous column
column(width = 3,
selectInput("Tic","Ticker",choices = c("","ALL",as.character(iris$Species)),selected = NULL)
),
column(width = 3,
dateRangeInput("Date","Date",start = '2016-01-01', end = Sys.time(),format = "yyyy-mm-dd")
),
tags$br(), # or just br()
column(width = 3,
actionButton("Submit", "Submit", width = "130px", icon("refresh"), class = "btn btn-primary")
# you may try smaller button with: class = "btn btn-primary btn-sm"
)))