Use FluentSMTP Plugin
Access the FluentSMTP by going to settings.
Select Sengrid
Enter the email of registered with Sengrid.
Enter Business
API key is the Sengrid Password.
Test
There is a tab that allows the sending of a test email.
Use Better Search and Replace (plugin) to replace the new email from any prior existing emails.
Change the Settings Administrator to the email registered with Sengrid.
Change the email address sent from the address in Forms.
Check the website for any possible locations for an email address.