If you have access to control design tools then you can tune the gain to stabilize the system. Depending on the design it may not even be possible for this to control the system.
If you have little knowledge of control I would try this. Seperate the filter to -> K -> 1/(0.001s+1) ->. Now replace the K (which should be a gain block at this point) with a PID Controller block which is in the Continuous Simulink library. Note: you need Simulink Control Design to do this.
Open the PID block. Once you've done that set controller type to P (this P is your gain, K). Now click the Tune button. If you're system can be stabilized this should in theory allow you to use a slider to tune your gain.
A couple notes on this approach:
1) This hinges on the fact that you have a model that can be properly linearized. This may not be the case. 2) You need the appropriate control toolboxes.
Good Luck!
