how to explode parts in solidedge when assembly is in .step format???

First of all you need to import the Step file into a Solid Edge assembly file.
Then in the tool tab, select ERA where u can perform the explosion.

Please remember that when you import an assembly , ALL parts are grounded and can't move. Ideally you should un-ground them and create relationships among the parts. The explode command would only work after you have some relationship between parts.

Hi, you have to convert from STEP/IGES into assembly format, save, and after to do explosion,