How to update a Git submodule if the repository and working directory are in different locations?

Question

git

The repository and working-tree are in different directories, there is a submodule in the repository, and it can't be updated.
I do like this:

$ git --git-dir=/var/www/colurgemgemru/data/colur.git  --work-tree=/var/www/colurgemgemru/data/www/colur.gemgem.ru/ submodule update

fatal: working tree '/var/www/colurgemgemru/data/www/colur.gemgem.ru/' already exists.
Clone of 'https://github.com/WordPress/WordPress.git' into submodule path 'wp' failed