I know how to DCA In, but how do I DCA Out?

People in here talk about DCA as a solid long-term investing strategy. I agree with this, and have been DCAing for the past few months with little monthly amounts into BTC, ETH, and some alts. It is a straightforward process.

What I don't understand as well is something I've heard around here about "DCAing out" especially during the bull run. I assume this means that each month (or whatever frequency), instead of buying say, $20 worth of Bitcoin, you instead sell $20 worth of Bitcoin.

If this is the case, then it seems that it's impossible to DCA in and DCA out concurrently (it'd just be a net $0). So when then, do you swithing from DCA In to DCA Out? Or, in simpler terms, when do you switch from being a crypto buyer each month to being a crypto seller?