Do nothing: In most cases, you should wait and be patient. Make sure that you do your technical analysis and have taken a position.
Re-evaluate your risk tolerance: Make sure that you reassess the risk tolerance, not based on emotion/feeling but through careful calculation.
Look at the big picture: Evaluate the bigger picture from both technical and fundamental aspects.
Research the fundamental reasons why the crypto is down: Make sure that why your portfolio is down. Not just the technical, but what factors are driving the trend such as back off of investors, regulation, scam etc.
Consider hedging: You can use various available tools for hedging
Diversify within crypto assets: You should rebalance the portfolio by selling one currency which is not performing well for buying a better one. Most currencies are exposed to similar risks.
Diversify across other financial assets: It can be a type of hedging. You can use assets such as bonds shares to distribute risk.
Add precious metals to the portfolio: Gold is particularly easy and saves to help you mitigate the risk.
Exchange with better crypto: You can swap the one which is not doing well by buying the one which has more potential. Again this would need thorough analysis.
Strengthen your current position: Even you should buy more if you think that the fall is a short term and there will be rebound. Warren Buffett is famous for buying more of a falling stock at cheaper prices when the markets drop.
Absorb the loss or quit: If you cannot absorb the losses, you can consider quitting the market.
Anthony