How can I modify an email template for migrated customers?

Im trying to send an email to my migrated customers to activate their account, ive got the bulk sender ready however i need to change the template to explain what is happening to my students as email is the only way some of them will know ive taken over the business from someone else and if they want their courses they need to activate their account on my new platform, websites etc are all new to me and liquid variables is something im yet to even get to grips with. can anyone help ?

How can I help?