If I understand correcly, you have a sample with an instrument sound, that you want to resample to a different (lower) pitch, while maintaining the playback speed and overall duration of the sample.
The operation you need is a frequency shift and you can find it (under that name or some variation of it) in most digital audio workstations or audio editing programs.
I'll take as an example the open source audio editor Audacity. Load the audio file of you sample into Audacity (assuming it' in a format recognizabe by the software, such as WAV or MP3), goto to the Effect menu, select Change Pitch, and set the parameters for your purpose.
As you can see, one of the options allows you to enter directly the current note and the desired note, as per your question (if I understood correctly).
If you're using a DAW, it should have a similar feature, look for Transpose, Frequency Transpose, Pitch Shift, Pitch Change, or some other variation of these names.