Open the Bitmoji app > Tap on the vertical ellipsis (the vertical three dots) at the top right hand corner > tap on Settings > Tap on Change Avatar Styles > You'll see a choice of Bitmoji Deluxe (the frustrating new one), Bitstrips (the one I went back to), and Bitmoji Classic. I too had your frustration and I finally found how to go back to my original one in an article after searching on the internet for way too long. When I went to settings, I then remembered that in the beginning there was always the choice between Bitstrips and Classic and I just didn't think to go to settings and see if I could revert to my former one (too ticked off that my old one seemed to be gone forever!), but you'd think they would have made going back to your previous avatar more obvious.
JQ
Open the Bitmoji app > Tap on the vertical ellipsis (the vertical three dots) at the top right hand corner > tap on Settings > Tap on Change Avatar Styles > You'll see a choice of Bitmoji Deluxe (the frustrating new one), Bitstrips (the one I went back to), and Bitmoji Classic. I too had your frustration and I finally found how to go back to my original one in an article after searching on the internet for way too long. When I went to settings, I then remembered that in the beginning there was always the choice between Bitstrips and Classic and I just didn't think to go to settings and see if I could revert to my former one (too ticked off that my old one seemed to be gone forever!), but you'd think they would have made going back to your previous avatar more obvious.