If you have the 'Git Graph' extension loaded in VSCode, click on Git Graph (on the bottom bar of the VSCode window) to open the list of commits. Image showing Git Graph is located at the bottom of the VSCode window

The graph displays a list of all commits for the project.

Right-click the commit you want to tag, select "Add tag" from the popup menu, then enter the tag details as required. You also have the option to push the tag: Image showing the tag details input options