If you have sold your crypto investment or you are certain some portion of the investment is worthless, you may report a capital loss for the portion you did not recover. And if you held the investment for more than one year, the loss would be long-term.
In TurboTax, report this activity under Wages & Income >> Investment Income >> Stocks, Cryptocurrency, etc. The loss will be reported on Schedule D, but capital losses are limited to $3,000 per year unless you have capital gains to match against your losses. Any unused losses are carried over to future tax years.