Kindergarten Theme is broken can't log in to WordPress at all

I have tried to log in to my site, which uses the Kindergarten theme. I cannot even log on and get the onscreen message:
`Warning: Cannot modify header information – headers already sent by (output started at /home6/techchal/public_html/afutureandahope/wp-content/themes/kindergarten/functions.php:221) in /home6/techchal/public_html/afutureandahope/wp-includes/pluggable.php on line 1207

the address for the website is: https://www.afutureandahope.org.il/

When you tell me how to fix this so I can log on, etc. Please be VERY specific in what I must do as I am not a techie!

Thank you