XMind for iOS supports updating the styles to all topics by one click. When you edit the styles of a subtopic, like text, color, branch color, etc., you can update the styles to all subtopics, or subtopics at the same level.
1) Select a subtopic,
2) Tap to open the format panel,
3) Edit the styles of the topic,
4) Slide down and you can find the button of Update Style,
5) Tap Update Style,
6) Tap Update to All Subtopics or Update to All Level X Topics.