Cordless blinds can often be fixed at home without needing to call the manufacturer or have new ones installed. Cordless blinds have an internal motor spring that retracts to hold the blind in place, and sometimes this motor needs to be reset for the blinds to work properly. In addition, the internal ribbons strung through the blinds may become tangled which again can be easily fixed.
Pull the cordless blinds all the way out, extending the blinds fully. This will help straighten out any internal ribbon components that are tangled inside. Pull the blinds down from the middle part of the blinds -- not the sides -- as that may only tangle the ribbons more.
Gently pull the blinds' bottom rail from the middle to reactivate the spring at the top to have the blinds recoiled.
Unhook the blinds from the mounting clips on your window if you are still having issues with sagging or no recoil on the blinds.
Remove the end caps from the head rail and look inside at the motor spring. There are various friction clips that help the blind recoil. Look for any damage to these clips, and if necessary contact the manufacturer for replacement clips.
Remove one of the friction clips inside if they all seem to be intact. The problem may be that there is too much friction, causing the blinds to operate in a rough manner. Repeat removing friction clips, one at a time, until the blind operates smoothly.