So you're locking your registration page. If you also want to hide the link to it in your theme's header, there is not an "automatic" way to do it. It can be done though! You'll just need manually do it by finding the link in your theme and commenting it out. The link will usually be in a file with one of the following titles (it depends on your theme):
Some themes have a different navigation for "mobile" so be aware of that as well: you might need to find them both and comment them out.
If you need some help with this, we offer this sort of coding as a service for no extra charge to our customer with a paid subscription to Locksmith.
Either way, you're always welcome to get ahold of us by clicking that chat button in the bottom right corner of the page!