I do not think this can be done out of the box using the current version of OpenFHE. You need Ring Switching to do that, and that is not implemented in OpenFHE.
Unless you implement ring switching by yourself, your best option is to instantiate the scheme with the larger ring dimension (2^11) and work with fully packed ciphertexts (2^10 slots) or sparse ciphertexts (2^9 slots) by clearing out any needed slots.
This thread might be useful to you. The authors claim implementing ring switching in their scheme using OpenFHE.