Q: how do i change the user on startup

You can select settings in the system to disable the Automatic Login on startup for all users.

Here's an example with text and images:

• Mac Security Tip: Disable Automatic Login - intego mac security blog:

https://www.intego.com/mac-security-blog/mac-security-tip-disable-automatic-logi n/

Similar, yet reverse context:

• Mac OS X - Enabling Automatic Login:

https://kb.wisc.edu/helpdesk/page.php?id=39258

Where there may be File Vault and encrypted content, you should read further & search

to see what else is involved so these items still work. Other issues may result in trying to

perform maintenance and backups if you have an encrypted file or vault in your OS X.

This mentions a certain issue regarding automatic login and file vault toward the end:

• Set your Mac to automatically log in during startup - Apple Support

In any event...

Good luck & happy computing!

Sounds like you have filevault turned on. The reason you could be having this issue is because the other user does not have permission to unlock your startup disk. Thats why you have to log into your account first, to unlock the disk. You should be able to grant the other user permission to unlock the disk in System preferences> security and privacy.

Use FileVault to encrypt the startup disk on your Mac - Apple Support