Child Theme Installed – Now I Can't Login

I tried installing a child theme using the directions on the wordpres site. I made a new theme called “infoway-child”, then added a “style.css” file, following the directions, and then when I tried to active it I got an error that wouldn’t let me login and the website was down. So I deleted the child theme and reinstalled my original infoway theme. I thought everything was back to normal but now I can’t log out. I get this error:

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/11060800/html/wp-content/themes/infoway/functions/infoway-functions.php:881) in /home/content/00/11060800/html/wp-login.php on line 368

I also can’t access my wp-login page. My site is https://www.andys-voice.com.

So I need to know why:
1. I can’t log in or out now
2. Why my child theme caused such a big error.

Thank you!