If you had not clicked “Save and translate” when creating your Taxonomy Term, then you will first click “Structure” within your admin toolbar.
You should now see the Structure page. On this page, click Taxonomy.
You should now see the Vocabularies page. On this page, click “list terms”.
Find the term you wish to translate and click “edit”.
In the local actions menu, click “Translate”.
You should now find yourself at the Translations page. If you had clicked “Save and translate” when creating your term, this is where you would have been taken. To add the French translation, click “add” at the end of the French row.
You will then be taken to the French edit form. Here change the English data to French data (Drupal fills in the fields with the English data, do not worry about remove the English). Then click “Enregistrer”. The French part of your term has now been created.