If you are a Crostini user then you will most likely be able to load Etcher under Linux and use it when Chrome OS 75 comes out - given that as I write this we are still on 73 you will need to do something else (like the alternative below) or wait
Alternately, You could use the Chrome OS recovery tool to write an image of your choosing. In step one you select the gear icon and choose use a local image (the image file has to be .bin) then continue with the process as normal