How can I get access to Git repositories in Redmine?

You can access the git repositories through HTTP or, if the SSL encryption is activated in hosting, access can also be done through https.
By way of example here we're using the TortoiseGit client to access a Git repository. The path to the Git repository can be found in Redmine in the settings of the project.
At Redmine project settings, click the Repositories tab. In the list of repositories you can see the URL for access. If not, click on Edit at the Git repository to see the URL.
If you see no URL, then some wnt wrong by creating the Git repository and you are not able to connect!

Redmine Git Repository Settings

There, the path is listed with the Git repository is reached.

Redmine Git Repository Url

Here that would be the URL:

In Windows File Explorer now is sufficient to right click with the mouse to bring up the context menu of TortoiseGit.

Git Clone under Windows

Git Clone with Source Url and target path

In the URL field, enter the URL to the repository. In the Directory field, enter the local destination path.
Clicking the OK button starts the Git client to access the repository. If a username and password is required, this will be queried by TortoiseGit.
TortoiseGit now access the repository with the given credentials, if the user have not enough permission in the repository you can see a error 500 in the TortoiseGit log. But - After the successful clone you can now find the files in the repository in the destination directory.