Terrain correcting a COSMO-SKYMED GEC image

Hello, I have a Cosmo Skymed image which is in GEC_B format (CSKS2). I have read into SNAP and compared the product against other projected data sets and note an offset. I would like to determine if the geometry can be improved with a terrain correction using SNAP. However, I believe the image is in projected coordinates and this prevents the process taking place in SNAP. The error message is:
“Source product should not be map projected”.
I see no tool to reverse a processing step so that I can complete the terrain correction and then convert from linear to dB. Any suggestions on how to tackle this is much appreciated.

Range Doppler Terrain Correction requires data which has not been rotated yet. Do you have the chance to get your data as SCS (Single Look Complex)?
Projected product levels have skipped the step of terrain correction already.

This is a possibility if there is not way to reverse the rotation (is it the same as ground to slant range conversion). If we do go down that route (a SLC) does SNAP support all of the processing to get the equivalent of the GTC image (Sigma0 or other) with Cosmo imagery in a Graph Builder? Do you know if there are other concerns about geometrical accuracy of Cosmo imagery (in GEC)? Thanks, Kevin

yes, you can then apply radiometric calibration, radiometric terrain flattening and range doppler terrain correction to get a radiometrically and geometrically correct image.
But the quality of the corrections strongly depend on the topography in the region and better results are achieved with high resolution DEMs (compared to openly available ones which are automatically downloaded by SNAP during these processes).