I dont know of a specific video that explains all this.. but if i was in your shoes.
first u need the sample.. u got that one.. so check
I bet, your not going to need to use the complete song. but a few fragments.
if you would slice your song with a grid.. your slices will make no sence what so ever.
so thats "kinda out of the question"
so...
learn how to add slice-points yourself.. (manual should do)
if you got a slice.. you can select it, and use the octatrack to "calculate bpm" (search manual)
Now play this slice, on your octa, make it fit with tempo-stretch / rate / pitch whatever
now SAMPLE your slice... your new sample will be manageable.
Do this for each "chunk of song you need for remix"
when you got all chunks.. simply load them in another project thats clean, or remove all tracks u used to slice/sample..
load up your fav drumrythms and synths.. add your song-chunks.. add a 303 and feel like norman cook
this is "kinda" the way i remix my old songs, where i do not always have the project files off anymore.. (used multiple drumcomputers and daws at same time.. so things got lost
enjoy mate