if you can still access /wp-admin/ you can just delete lay theme in appearance → themes. and then re-install it! you can go to laykeymanager.com to download lay.zip if you don't have it. all of your data/content and settings will stay the way they were before.
if your website shows an error and you can't access /wp-admin/ u can try this:
"First try this: Access your FTP server. When you login to your webhost control panel you can probably use WebFTP right in your control panel. Or you can get your FTP login data in your webhost control panel and use FileZilla to connect.
Now find your website folder and inside go to: "wp-content" → "themes". In here find the "lay" folder. Rename it to something like "_lay".
This will disable Lay Theme. Now see if you can access your website and /wp-admin/ again.
If that didn't change anything, try the next fix: "If the issue is caused by a Plugin"
If it worked, login to /wp-admin/ and go to "Appearance" → "Themes". In here click on "Lay Theme". Then click "Delete" at the bottom right. This will not delete any of your settings or content, as these are stored in the database and in your uploads folder, not in the theme folder.
Now get your lay.zip file. If you don't have it on your computer search for an email by laytheme that contains a link to it. If that doesn't work write an email to lostfiles@laytheme.com with your key or tell us the email address you used to purchase lay theme. If your Lay Theme version is very old and that causes an issue, you can also get the latest version by emailing lostfiles@laytheme.com.
Now in "Appearance" → "Themes" click "Upload" at the top and choose "lay.zip". Upload your zip file and activate Lay Theme."
From:
https://laytheme.com/troubleshooting.html#critical-error
if it doesn't work you can also send your ftp login and website url and a link to this topic to info@laytheme.com
sorry for the late response