If you search "<song name> bass tab" or "<song name> bass cover" you might find some helpful stuff, but be aware that a lot of tabs are full of errors, and some are very badly laid out. so look at a few and find one you are comfortable with.
It's worth watching a Sabbath live video and getting an idea of what Geezer is playing - how busy he is(n't) and where on the neck (about 5/7 fret IIRC). Listen to the song and try to hear what the bass is really doing, not what you thought it was doing. Tab can be great for understanding fills.
When learning, start slow and build up. Concentrate on getting the notes of each part right, then getting the right rhythm, then getting up to speed. Don't be ashamed to just play the root notes without any fills to help you learn the changes. Try to hear how your bass blends with the music when you are in time and in tune.
If you start making repeated mistakes, take a break so that you don't 'practice the errors'