You will need to modify the email template(s) -
manual.limesurvey.org/Email_templates
Here is a fairly comprehensive article on email style best practices - www.emailonacid.com/blog/article/email-d...-best-practices-2017
Here is a fairly comprehensive article on email style best practices - www.emailonacid.com/blog/article/email-d...-best-practices-2017