Corrugated plastic roof flashing - no clearance

I'm looking to replace the plastic roof on a large lean-to shed. The shed is against the garage and the roof is tucked in just below the slates on the garage roof.

Doesn't look like enough room to get any flashing in there. The existing roof has somehow been bent up, but not sure how that was done.

Any ideas what my options are? Thanks

If you put the ends of the new sheets on a piece of 3x2 and lay some weight across it in a uniform manner to make some stress you can then apply gentle heat with a heat gun and it will start to curve.

Love the Fred flinstone supports.