Hello Tia
If you want to add slider images then you will need to follow the steps below
Go to dashboard > slider > add new > add title/description > add featured image > click on publish/update
repeat the step to add another image for the slider to slide.
You can not add multiple image at once for slider.

You may use our full documentation on how to customize or change things on our theme click on the link below to see
https://luzuk.com/demo/multi-mobile-app/documentation/
If you are unable to add images in the slider then send us your wordpress username and password, website link on [email protected] we will do it for you.
Thank you