Depending on the WAY in which it is "uncomfortable":
Let's face it, an enema is going to be uncomfortable in one way or another. I have experienced some aspect of EVERY enema I have taken that was "uncomfortable" by some definition
If it is simply hard to hold, there are techniques like deep breathing and bite rag you can use to get through it.
If uncomfortable means light to moderate pain during the early to middle part of retention, you probably want to just tough it out.
If the pain is severe, you have likely taken too much! Dump it and start over
If it actually causes nausea, again light to moderate is to be expected. If you come anywhere close to vomiting you need to wait longer after eating, and wait longer between rounds. You might need to dilute the solution with more water.
If it just leaves you feeling "Ragged" it's likely electrolyte depletion. Some Gatorade/Powerade helps, Pedialyte if you can get it helps more.
Also AFTER you are finished, fruit like bananas or peaches that Are high in potassium can help as well.
Also, you can minimize discomfort by doing things like taking the enema in a place ou are comfortable lying down resting and have rested there many times.
Choose a position and stay with it until it's time to run!
RELAX!! No hurry! Clear the schedule, eliminate distractions.
Before getting in position, pee!! That insures that the bladder is not ADDING to the pressure on the lower abdomen.
Eliminate ANYTHING that puts pressure on the lower abdomen.
The water should be warm but not hot to YOUR touch.
REMOVE any shapewear. If you are female a bra that does NOT interfere with your breathing can stay on or not It's your call. One that interferes with your breathing AT ALL should come off A bath robe or knee length dorm shirt or nightgown works so you don't have to be completely naked.