Firesub supports import from any text based application, e.g Microsoft Word, Microsoft Excel, Microsoft OneNote, Pages for Mac/iOS, Numbers for Mac/iOS and a lot more.
To import your checklist, first create a new template without any tasks.
Then open the document or application where you have your current checklist and copy the list of tasks.
Paste the copied checklist text into the text field Add new task... Firesub will automatically recognize you are importing a list of tasks and will be formatted accordingly.
After confirmation, all tasks are imported and you can make changes to the tasks as you like.