Also, depending on what you have done here you can use code to adjust your slider as shown here.
https://www.wix.com/corvid/reference/$w.Slider.html
If you have simply used the slider element from Wix Editor, then you are only able to use what settings there are for the element itself.
https://support.wix.com/en/article/adding-and-setting-up-a-slider
If it is more an issue with how the slider element is displayed on mobile compared to on desktop for example, then you are better suited going through Wix Support as that is not a code related issue.
https://support.wix.com/en/article/contacting-wix-customer-care-for-support