Hallo,
in few words:)
IDD contains a merge groups of surface, that you se as violet lines and in model tree for idd you see it as one component
firs step if there is problem is detach one single surface-you can go with cursor on that surface in workspace or in model tree and click on it and then use function detach, same you achive if you drag and drop it in tree out of component structure... if you finish you see in tree one component compound of remaining surfaces and detached surface, in work space will be border between this two yellow
same way you can select them in tree as well as on model with control and then use merge function to join or merge(i hope you know how it work-i use it due triing all posibilities and using prewiew)
last think is that sometimes it isn`t possible to merge two groups and last posibility is combine it
you can use function or drag and drop all surfaces in one component to other
sometimes it help and sometimes gaps are so big or some curves are bad
***if there are small gaps or other problem this can solve it
i don`t know why, but sometimes it works better then auto repair
main reason is repair can cause gaps anywhere in model
this method can cause gaps only if some edge is problematic, but advantage is, that if remain one, you can try repair or detach again last two surface and it can works
