On a machine that has an Internet connection, pull and save the support bundle image:
docker pull replicated/support-bundle
docker save replicated/support-bundle > support-bundle-image.tar
Then copy the tar archive to the airgapped server and run these commands:
docker load < support-bundle-image.tar
docker run -it --rm \
--volume $PWD:/out \
--volume /var/run/docker.sock:/var/run/docker.sock \
--net host --pid host \
-e HTTP_PROXY -e HTTPS_PROXY -e NO_PROXY \
replicated/support-bundle generate