The GIF below shows how to delete a Working Time in your Calendar :
You can follow the same steps to delete an Unavailable Time.
To edit a working time, you can click the pencil icon next to the dustbin icon shown in the GIF above (we have an article here showing how to edit a working time).
If you will be unavailable at a certain time on an ongoing basis, eg. if a non-Harley Therapy client has reserved a particular time for their sessions, then it is easiest to edit or delete the working time so it is removed from your availability on an ongoing basis.
You would be able to add the working time back to your Calendar if the slot becomes available to book again in future.