1) Embed the riff in a MusEdit document (use a link to the file) as described in How to embed a sound in a MusEdit document.
2) Insert a Tab line (Ctrl+A), play the sound sample by double clicking on it, then try entering the fingering you think is correct on the tab line.
3) Make note stems visible on the tab line with: View | Show Note Stems on Tab and then add quarter, eighth, sixteenth... note stems to the Tab fingering to get the timing right. Use selection and Options | Join Note Tails to tie notes together where appropriate.
4) Play the music on your guitar or play it as MIDI sound via Options|MIDI|Play Current Document.
5) When the tab version sounds right select the tab line(s) and choose:
Options | Tanslate Current Line(s)... | To Treble and then the treble
version of your tab transcription will appear below the tab lines. You
can now print out both the tab and treble transcriptions if you wish.