After seven months off, you will have lost a significant amount of fitness. How much is hard to say. It depends on your training history. If you’ve been training for decades, then it should come back fairly quickly (within months). If you’re relatively new to structured training, then it will take longer.
As for intensities, I would start with a drift test to determine your current aerobic threshold. Detraining tends to skew intensity toward the anaerobic side, so your AeT HR at the moment is likely lower than what it was.
Most importantly, don’t make the common mistake of trying to “cram”. You can’t speed up the process by upping the intensity or over-doing it on duration. That will only set you back further. If you’re patient and progressive with it, you’ll get the best results you can.