cannot modify header information error after move to new server

I moved my site to a new server and new domain name. I downloaded all the wp files and then uploaded them to the new server. I downloaded the database and changed the domain name within database to the new one and uploaded to the new server. I edited wp-config for the new site. Now when I try to access the site I get this error message:

Warning: Cannot modify header information – headers already sent by (output started at /home/content/84/4819084/html/site/wp-content/plugins/smart-youtube/smartyoutube.php:1435) in /home/content/84/4819084/html/site/wp-includes/pluggable.php on line 865

I’ve seen support topics on this error indicating that spaces may have been added to the pluggable.php file but I did not change pluggable.php in any way so I don’t see how that could have happened.

I cannot access wp-admin to try to diable plugins.

Site address: https://www.seattlewcswing.org/site

Any help would be appreciated.

Bonnie