My advice would be to use Eternabond on the roof when possible.
Did you check
Youtube for tips on applying caulk?
I wash the roof with dawn and water, rinse and allow it to dry. Then I remove the loose caulking, clean the area well with lacquer thinner and apply the new caulk over the old.
If you want to remove the old caulk, use a heat gun on low and a plastic scraper. Some use a multitool and have good results.,
Take your time, it's not difficult.
Dicor self leveling is an excellent choice for horizonal surfaces.