Making your Tumblr blog private is a simple process. All you need to do is follow these steps:
1. Log in to your Tumblr account.
2. Click on the “Your Blog” link in the top left corner of the screen.
3. On the right-hand side of the screen, click on “Privacy and Security”.
4. Under “Privacy Settings”, you will see a button called “Make My Blog Private”. Click on this button to set your blog private.
5. Click on “Save Changes” to confirm your privacy settings.