What are the stains?
Do not touch it - take directly to a reputable dry cleaner that specializes in wedding dress preservation.
What is the fabric of the dress? What is the stain? Honestly I would take to a dry cleaner that specializes in wedding dress preservation and let them handle it. I still have my mom's from the 50's. Too bad she was a size 4 and 5'1".
Take to a dry cleaner that specializes in formal wear. If it can be fixed, they can do it. Will not be cheap, so be prepared for a hefty bill. Do not try and treat yourself as that may diminish the chances of a reputable dry cleaner to get it out.
You didn't say what caused the stain, so I will give you several videos to choose from. I hope the stain completely comes out.
Because a wedding dress is such a special garment, I'd leave cleaning it to an expert. Look for a dry cleaner in your area that specializes in this process. The price will vary (material, number and type of stains, etc.) but it's totally worth it!
A dirt stain can be stubborn, especially from a floor. I would be hesitant to tackle this because wedding dresses are an investment. Bottom line is find a reputable cleaner who does a good volume of wedding dresses. That is worth the money to have quality results and have your worries settled.
Best wishes to you and your new husband