When the markets are down its the perfect time for investors. Like Warren Buffer said "Buy when there is blood on the streets". Every major cryptocurrency will come back up believe it.
Unless it goes down, in that case just hold or keep buying
This is a typical trading scenario...
Remember you don't lose or win until you sell, so keep holding until conditions get better, but take the chance if you still can.
"Never invest what you cannot afford to lose"...
This way you won't pay it much attention when it goes down, and can calmly wait until conditions improve, no matter how long it takes. Panic sellers are the ones always losing.
Of course there are some assets where you can be confident things will improve, like Bitcoin, while some altcoins on the other hand... You would be wise not to expect recovery from those anyway, and its best to avoid getting in those in the first place. But in case you were gambling it, just set up a sell order at some point above the price at what you bought in, and hope someday it triggers.