Start off by pre-vacuuming the carpet well. Make plenty of slow north-south east-west vacuum passes.
Then clean with a strong mix of Encap-
HydrOx. Here's a cleaning process that works well on problematic CGD carpet:
1. Very quickly run over the carpet with your Cimex, rotary or orbital machine - dispensing the solution as you rapidly cut across the carpet.
2. Then go back and slowly scrub over the carpet again, beginning from where you started your first pass. Cover the entire carpet making a couple of slow dry passes. You can feather just a slight bit more solution as you make the slow scrubbing passes. But be very careful that you don't over-wet the carpet (more is NOT better).
3. Finish up by post-bonneting the carpet with a damp bonnet.
4. Put fans on the carpet to accelerate drying.
That approach will usually nail even the worst offending CGD carpet.