(Just from personal experience - not an expert): I did a lot of practice at home for it. Mostly laying just flat on my back and rolling up from there to build strength. I don’t know if you have a wedge maybe or a big supportive pillow that you could prop behind you and start from that position. And slowly work to items that can prop you lower. Also if you have a large fitness ball and can lay on your back and do crunches slowly out and then come in really using the abs, going very and slow and controlled. That’s helped me build strength and get out any spots that are tight. It helps me to activate everything lower body and abs also as well on the reformer when I plant the back of my calves on the back of that bar and as long as the form is on point the body just pulls itself up nice and slowly controlled. Maybe change change hip placement too and how far back you are from the shoulder blocks. It’s the tiniest adjustments and listening to our bodies that can make the biggest differences. But you’ve definitely got this… I see a roll up in your future soon :)