importing sub assemblies?

Insert, Component, Existing Part/Assembly

Insert the assembly using same process as inserting a part
After assembly you can configure as flexible if needed.
Mate as you would when inserting a part
There are no mates to lose

Hi If you mean the sub assembly is frozen and the mates do not work, highlight the assembly in the tree and and click properties. Then unfreeze the file. Then when you go back to the main assembly the sub assembly will move using any mates you have incorporated. Otherwise the sub assembly will be frozen and merely treated like a part . Not sure if that was your query? Paul