S.R.
For those who don't know, a sewer ejector is a large pit in the floor with a special pump that collects waste from plumbing fixtures and pumps the waste water up to a drain line. An ejector is installed in a low spot of the house where gravity draining is not available. It's a good solution for places that could not normally have a bathroom. But, as the question suggests, there can be some odor issues to deal with, along with the dreaded pump failure. So they do require maintenance from time to time.
All sewer ejectors need to be installed with a "local vent," that is, a vent line that goes from the pit to the outdoors with nothing else attached to it. You may have a venting issue that needs to be addressed, but first check the most common cause of ejector odors: bad or missing seals.
On the lid of the pit itself there should be rubber seals between the lid and the pit housing and also around the discharge line and vent line coming through holes in the lid itself. If you suspect the seals are not containing the pit odors, unplug the pump and then unbolt the lid and inspect all the seals for damage, and repair them or install new seal rings. I must caution you that for obvious reasons working on a sewer ejector pit is not a job for the faint of heart. Take my advice from personal experience: This is one of those jobs where it's money well spent to have a plumber do it for you.