Please refer to the tutorial "Rotating and Translating a 3D model with CraftAR Augmented Reality SDK
" to get an example on how to rotate a 3D model. As you can see, the method setRotationMatrix takes as argument a 4×4 Euler matrix that can be obtained through the method Matrix.SetRotateEuler.
This aside make sure that you are adding the 3D model content you are transforming programatically as it is shown in the example “AR programmatically”: https://github.com/Catchoom/craftar-example-android/blob/master/craftarexampleandroid/src/main/java/com/catchoom/craftarsdkexamples/ARProgrammaticallyActivity.java#L166
If you are still experiencing problems after this please give us some more details regarding if the problem is only transforming the model content but it does appear in the scene and if you see any error messages in the log.