I appreciate your patience. Sorry for not providing a response in time.
I suggest you use HFSS 3D layout to import the GDS file and verify if the model is imported correctly by validating the nets and other components. Please share the error you were getting while doing so.
After the validation is complete, then you can use Q3D to extract the RLGC. Do you mean the equivalent circuit when you refer RLGC of your model?
The Q3D solution frequency has to be set as per the device's operating frequency.