Rebalance or HODL ?

I am investing from last 5 years, so please bear with me that I might not know all the nuances of investing. Currently, the strategy i follow is sip + lumpsump whenever i get, invest in mutual funds and ETFs. The classes I invest in are large caps, mid cap , small cap fund ( one each ), a gold and US fund. One thing I never thought about was how to rebalance, i dont book profit properly, most of my gains in small and mid caps have been wiped. I am thinking should i book some profits on gold and US funds given I learn something from my small cap/mid cap funds. But where to invest that ? In general, how do you folks book profits and rotate between classes? Please share any system you follow for the same ?