Using your terminal history can save time or help you to remember commands you have not used in a long time. If you make typos in fish they still go into your history. There are a couple of ways to remove commands from your fish history.
Get a list and delete some or all of the commands that match the string:
history delete --contains "search string"
Open your history file. You can delete the command and time stamp for any commands you want to remove.
wipe everything clean: