The treatment depends on the cause, but normally these things are fixed by reversing the problem (if possible).
For example, eating less salt, placing a cold flannel on your eyes after crying, letting your body get rid of any alcohol you’ve drunk.
Puffy eyes are sometimes a sign of an underlying medical condition, especially if it is causing you pain or discomfort.
In this case, see your GP and they may prescribe you something to reduce the puffiness.
If you have hay fever, antihistamines or eye drops are normally the go-to.