Can I re-lactate? Advice please!

I need a little guidance, my daughter is 8 months old and I tried to breastfeed but I couldn’t get the hand of it. My milk has dried up almost 3 weeks after having her. We’ve always had problems finding the right formula for her. I know since she’s been bottle fed almost completely her whole life. I have a breast pump but have no idea on where to even start on learning how to use it. Has anyone ever been able to successfully relactate after such a long period of time? If so can I have some tips/tricks.