If you do it yourself, do it outside in the sun on a warm day. This will help the gasket stay pliable. Take your time, use the right tools and only slap the windshield with a flat hand. Don't scrape the edges of the windshiled with your tools and don't pry on it. 2 people works best, but keep your eye on your partner if they don't have experience. Better conservative and time consuming than aggressive and in a hurry.
