Long-term investing, when to sell?

Hi so I've recently started investing, my plan is to invest long-term and have it grow over the years. My portfolio consists in some individual stocks of companies I believe in and some well performing etfs. One of the stocks I own has suddenly spiked almost 10% (Xiaomi I believe due to the new electric car release).

I don't know whether to sell those stocks and reinvest in another place, or keep them as 10% growth is what I expected to gain in the long-term. In general I would like to know the best strategy for when to decide to switch the investments (as I still don't need to cash out the money I invested).

Sorry if this question has been overasked, thanks in advance.