Use ta.stdev

something like that:

//@version=6
indicator('D O', 'D O', true)
[do_1] = request.security(syminfo.tickerid, 'D', [open], lookahead = barmerge.lookahead_on)
plot(do_1, title = 'Open', color = color.new(color.yellow, 0), linewidth = 2, trackprice = true)


lookbackInput = input(5)

var float doStdev = na
if do_1 != do_1[1]
    doStdev := ta.stdev(do_1, lookbackInput)
    doStdev

plot(do_1 + doStdev * 0.59)
plot(do_1 + doStdev * -0.59)