I tried isopropyl, acetone, but nothing helps. I didn't use hot air much, since the compound is thermal resistant. Any ideas? Thanks!

 

The likely epoxic white compound will take sophisticated chemicals to dissolve, with partial success to remove the heat pipes. The IC itself is likely a ball grid soldered to the board with need of even more sophisticated desoldering equipment and training to do it heating both the board and the IC.
And more likely, to be a hundred times more expensive task to remove than replacing the entire assembly.

 

The only way to remove it will destroy the chip and any information under the coating. Had the people who put the coating there wanted you to know what was under it they would have told you.

Ron