flyctl release 0.0.311 got this:
$ fly releases --image
VERSION STABLE TYPE STATUS DESCRIPTION USER DATE DOCKER IMAGE
v424 true release succeeded Deploy image your@email 1h52m ago registry.fly.io/yourapp@sha256:e09f0e9030939d9f90dfdfbbac9bca9bc3v8b4340acfede0f39
Then you can deploy again with fly deploy -i registry.fly.io/yourapp@sha256....
Not that this will only bring you back to the previous Docker image. It will not revert changes to secrets or anything set in fly.toml
.