Your duct flange is not a pipe hanger. Stop before it gets buried, document the conflict, and coordinate clearance/support instead of letting the pipe load or vibrate against the duct.
Do not let another trade use your duct/flange/hanger as support for their pipe or cable.
Check
Take photos showing the pipe resting on or touching the flange.
Check whether the pipe has its own hangers/support independent of your duct.
Check duct hanger rod length/elevation and whether a safe drop/offset is possible.
Check ceiling height, grid, insulation, vibration, and access impacts before moving anything.
Notify your foreman before the conflict gets covered by ceiling or insulation.
Steps
Take photos showing the pipe resting on or touching the flange.
Check whether the pipe has its own hangers/support independent of your duct.
Check duct hanger rod length/elevation and whether a safe drop/offset is possible.
Check ceiling height, grid, insulation, vibration, and access impacts before moving anything.
Notify your foreman before the conflict gets covered by ceiling or insulation.
Say this to your foreman
The sprinkler main is sitting on our TDC flange at [location]. I checked our hanger elevation and their pipe support. Do you want this coordinated with sprinkler, or should we drop/offset our duct per an approved detail?