Newbie problem with tags

Hello to everyone.
I am a total newbie to Kodi having used Plex for several years I am not happy with the direction they are taking.
I am using tags in my TV Shows to group together shows of the same subject i.e. cooking.
I know I have the naming correct on several shows as they appear and can be viewed in such areas as Lists, Titles etc.
However when I try to assign them to an existing tag they don’t show in the add to tag list.
All and any ideas welcome.