You can look at the historical trend of funds and the performance of fund managers. If it is a good fund, don't worry. According to their own pre-set, the decline is just a good time to add positions. You should double the number of shares you buy, so as to reduce the cost and wait patiently for the future rise.
If the historical trend of the fund is really bad and the performance of the fund manager is not so good, then it is time to break it, sell the fund and re-select a good fund for investment. There is no need to waste energy on junk funds.