You and your teammates must be in a group in Moodle before uploading your group submission. The assignment submission point will normally be set up so that one member of the group can upload a file or submit a link on behalf of the whole group.
Go to the submission point and choose Add submission.

Drag and drop or browse to upload your file, then choose Save changes

The assignment status will show Submitted for grading. The file will be uploaded for all members in your group.