Assuming that (it's not clear from your question):
- you change htaccess to redirect http request to https (best way, IMHO). Lots of googles on that; your hosting place should also have guidance specific to thier hosting environment.
- you changed the two URLs in the wp-options table to show the full URL with https
That's all that is really required for https, assuming that your hosting place has properly installed the SSL certificate.
If you have done the above, then please edit your answer to provide more (and detailed) details about what you have done so far, and what doesn't; work.
Note that will also need to do a search/replace for http://www.example.com replace with https://www.example.com . In particular, the media library items in the database will have the old URL. Lots of plugins to help with that; I like the "Better Search and Replace" plugin.
Of course, backups of database is always important when making changes.