You need to give some idea of what you have tried so far, and how familiar you are with the charting tools, especially REAPER. If you are familiar with REAPER’s plug-ins, you can enable ReaSynth on your vocal track’s MIDI, then use that to find pitches by ear (and if you’re using the REAPER template for C3 customs, you’ll find ReaSynth is already enabled on the vocal tracks). If you know how to read music, you can also try looking for sheet music. Depending on the how faithful the sheet music is, you’ll still need to massage your chart to get exact timings, proper slides from one pitch to another, and so on, but even the most basic sheet music arrangement can serve as a good starting point.

If this doesn’t help get you going, provide the details I mentioned above and there will be a better chance to push you in the right direction.