Stop the cover-up before the damper, actuator, link, or access side gets buried. Mark the location, document it, and get the access opening framed per the approved damper detail and AHJ/code requirements.
Check approved damper submittal, access detail, and rated assembly requirements.
Mark studs/ceiling/grid with clear location before the work is covered.
Take photos showing damper and surrounding framing.
Notify foreman before the other trade closes the wall or ceiling.
Say this to your foreman
Drywall/ceiling is about to cover the damper at [location]. I marked the damper and access side and have photos. Do you want me to stop cover-up until the correct access opening is framed?