3D models stored as STEP product data files (.stp, .step) are rather common sight and well supported in various 3D modeling tools, so you should have no trouble finding a tool capable of translating .step files to .dae files that are for Collada 3D Digital Assets.
Open STEP file Open DAE fileA Mac version of the popular 3D visualisation software
A 3D product data optimalization software
A converter for 3D formats
An online CAD conversion service
An open source multiplatform 3D CAD/MCAD/CAx/CAE/PLM modeler
A commercial online CAD converter
A 3D CAD translation software