Your ring will no longer hold a diamond. I suggest you put substantial effort into finding it so you can have it reattached. Retrace your steps and all that.
You go to the jeweler and pay for a replacement
So sorry to hear this.I pray you find it somehow.
I never found mine.
Well if you have it insured, your insurance company will find a correct replacement and then have it set for you, Just as I did, I lost my diamond from my ring last year and insurance covered the cost of a replacement mind you the diamond was a high grade white diamond 0.49 ct, so I was grateful I had the for thought to insure it. If you are not insured please follow instruction from the first answer from uni2. Sharonf