Hello @eppikyw,
To remove the author name and the post date in the single blog post add below given CSS by going to Admin Panel > Appearance > Customize > Additional CSS.
.single .entry-meta {
display: none;
}
To remove the category you have to activate the child theme. To know how you can create and activate the child theme please refer to below given link:
https://wptravel.io/how-to-create-a-child-theme/
After activating the child theme in your child theme functions.php add below given code.
https://pastebin.com/dp9wywNb
Hope this helps.
Thank you.
Best Regards!!