The GIF below shows how to edit an existing Working Time in your Calendar :
You can follow the same steps to edit an unavailable time.
Working times are the slots that will be shown as available to new clients in your public profile. We have an article here showing how to check what times are being shown as bookable to new clients in your profile.
If you are receiving an error (such as an error regarding overlapping working times), we have a help section specifically for Calendar errors here.