In earlier, We have the option to demote the site links through the Google webmaster tool. But Google has removed since 2016 that option from the webmaster tool. Here is the reference to get more details: Visit here.
Sitelinks are automated, these are created through website best practices and Google doesn’t tell us how to create the sitelinks or control their appearance directly. which means there are no steps that you can follow to get the sitelinks for a website but we can follow a process to increase the chances of getting Sitelinks. see the google recommendation:
We only show Sitelinks for results when we think they’ll be useful to the user. If the structure of your site doesn’t allow our algorithms to find good Sitelinks, or we don’t think that the Sitelinks for your site are relevant for the user’s query, we won’t show them.
There are best practices you can follow, however, to improve the quality of your sitelinks. For example, for your site’s internal links, make sure you use anchor text and alt text that’s informative, compact, and avoids repetition.
Hope you can understand, still, you have any doubts, please let me know.