When should long-held alt coins be sold? When to sell even when we are in profit? That doesn't make sense. Let me know if there is a suitable alternative to this issue.
The step you have to do is to understand the market, you can do research first. Monitor the price movement in the past.
Recognizing recurring price action patterns or Price Action setups reflects a change or continuation of market sentiment. The more you understand how the market works, the more you have an idea of the profit ratio when you enter and exit the market. That way you can conclude when the right time to hold and sell the altcoins you have.