Exporting the map for stream order

Question

I have written a code for estimating stream order of an area (ROI) . I want the particular geometry to export it as an image to drive. But I could not do it..Can anyone help me?

ROI 
List (5 elements)
0: [85.63695258708094,23.126852581335314]
1: [87.96605414958094,23.126852581335314]
2: [87.96605414958094,25.251284261753156]
3: [85.63695258708094,25.251284261753156]
4: [85.63695258708094,23.126852581335314]

var order_hack = ee.ImageCollection("projects/sat-io/open-datasets/HYDROGRAPHY90/stream-order/order_hack");

var style = require('users/gena/packages:style')
var palettes = require('users/samapriya/utils:palettes');
Map.setCenter(7.926, 59.570,8);
style.SetMapStyleGrey()

Map.addLayer(order_hack.mosaic(),{min:1,max:10,palette: palettes.extra.blkred}, 'Order hack');
Map.addLayer(ROI)
Map.centerObject(ROI,10)