Found a good one available on testing/bookworm.
https://tracker.debian.org/pkg/golang-mvdan-sh
on a debian testing enabled dev machine:
sudo apt install golang-mvdan-sh-dev shfmt
I recommend reading the man page for shfmt.
Good options:
shfmt --indent 2 --space-redirects --switch-case-indent FILE
use -w|--write to write to file.
The above is for formatting from the command line.
For the future, during development, editing files, I recommend https://editorconfig.org/ and use an editor that support editorconfig (many does), with this, when saving the file, editorconfig will correct the format.