If the slides come from Blackboard and you are writing for an audience with access to that resource (i.e. your lecturer), provide the name of the site and the URL. If the audience for which are you writing does not have access to the slides, cite them as a personal communication.
Cite information from your own personal notes from a lecture as personal communication and refer to it only in the body of your essay (see Personal Communication section).
See also the guidance on the APA's Style website at:
Jenkins, R. (2020, April 15). Lecture 7: The development of language in children [PowerPoint slides].
Presenter surname, initial(s). (Year, Month Date). Title of presentation [PowerPoint slides]. Platform. URL
Winkleman, N. (2019). The language of coaching: A story about learning [PowerPoint slides]. SlideShare.
Presenter surname, initial(s). (Date). Title of presentation [PowerPoint slides]. Site name. URL