Use an email builder to recreate 5 emails created in MailerLite

I have created five email templates in MailerLite which I can share links to. I want to stop using MailerLite for these emails and instead have my own HTML templates that I can reuse. I have found an HTML builder that I want to use (below) in future but would like the admin of copying existing emails over to this new style of template done for me to save time. The templates don't need to look identical, just have the same information shown in a logical, good looking way.

Using this email builder - log on can be provided in order to save the templates: https://bigbangthemes.net/BBT_Builder/template/sion/