Disguising the identity of a voice over
You have a few options for disguising a voice, but several of them intentionally make the sound unnatural.


Have someone else record the voiceover. This is the only technique that results in a truly natural sound because it is an unmodified voice. There are some relatively inexpensive voiceover services available if you don't already know someone. Because the person is never seen on screen in what you describe, you don't have to worry about lip sync, just rough timing.
A simple pitch shift. Change the key of your voice with a pitch shift filter and correct the timing. This is easily reversible if you have serious concerns about your identity. This video describes how to do that in Premier.
Randomize the pitch shift, layer multiple pitches, or add other distortions. Sound designers get creative with plugins.