I heard that there is a form that can be filled with the IRS to request some change to tax status that will allow a tax payer to claim all capital gains lost in the current year rather than stretch it out over time. What is that form?

I trade the stock market and have large losses that have accrued over the years that I would like to take as a lump sum instead of stretching it out over several years. At the $3,000 per year rate I have looses that will take the next 15 years to write off.

Thanks in advance.