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If you have access to a weight assisted pull up machine, you can do that. If not, you can substitute lat pull down machine exercises for it.
Last resort and a real good one for building up to your first pull up is to do negatives. Use a bench or step to get your chin above the bar and bend your knees so that you are using your muscle strength to lower your body until your arms are straight. Also, I would start with your grip shoulder width apart instead of wide grip as wide grip is pretty hard to do. Do the amount of reps specified. Good luck. :-)