It is not straightforward to repurpose Skills developed for other platforms, like Amazon Alexa, for Mycroft. The key reason for this is that other platforms use different programming languages. For example, Amazon Alexa uses the Lambda language and is tightly integrated with the Amazon Web Services platform.
That said, having the structure or logical flow of your Skill well defined already makes it easier to start development of your Mycroft Skills.
Want to know more about Mycroft Skills? Ask our friendly community over on Mycroft Mattermost Chat.