If there is no simple fix like making the medikit texture transparent (no 3DsMax involved) then this is a question that has no simple answer.
You should really try to find some good tutorials first. There is no simple way to do this, you need to understand the principles of 3D modelling , character rigging and compiling for the specific engine.
You would learn how to get the model from the game (decompiling) with certain tools, how to convert them to a format that 3dsmax can read and then proceed to edit the medikit out of the mesh.
This process might require you to repair the mesh (holes where the medikit was for example), maybe edit the texture or shaders that are udnerneath it etc etc.
Then you would need to convert it back to a format that the source engine accepts, compiling the new model and replace the old one.
It is a process that involves many many different techniques, so you would need to start to learn all of them.