If you keep the PC, you can purchase a Corsair H60 for an AIO.  It also uses an Asetek pump, and the radiator is the same dimensions, so it also fits in the OEM radiator box up top.  The hoses are longer though. So you'll just have to deal with some slightly restricted airflow. 
So I received my air cooled Aurora R10 with the R7-5800 and RTX 3060 Ti last week. I noticed after a few days I was getting micro stuttering while playing games. I downloaded HWMONITOR and noticed my CPU was running at 97C. I played around with fan settings with no help. Paid just over $2400 for this rig Fast forward to today and I call tech support, they update the bios (like this is the problem) and then stress my cpu with the Dell program. I was kind of laughing while this was going on as the CPU stress only had it running at 3700MHz so of course it only got up to about 85C. We load up a game after I question this and of course it gets up to 97C. They install HWinfo to log data while I play my game and after analyzing it say it is thermal throttling so they will send a tech to come change out the cpu heatsink/fan and add thermal paste. I am sorry but this cooler they have in this Aurora R10 is not meant for this CPU in this case, it is horrible. Changing out the cpu cooler and adding new thermal paste is not going to fix this problem. I argue this point to deaf ears. If you look at the cooler is is a rounded piece that sits on the square CPU. It looks like an Intel cooler. It doesn't even cover the entire CPU, its like a $10 cooler in a $2400 computer. I reached out to sales to get an AIO and VRAM heatsink mailed to me. Of course they dont have the AIO in stock but proceed to tell me that the VRAM heat sink is like $22. I was floored they were going to charge me for these heatsinks after the problems I had. I ended that call quickly and called customer care to look at returning the computer. After talking to customer care I notice the same computer I have is $2000 dollars so they tell me they will give me a credit. I tell her to use the credit to send me an AIO and the VRAM heatsink and I would be happy. She can't do that so we talk about returning and reordering a new one. For curiosity sake I price out the same computer but with a RTX 3080 and of course its only $300 more than my purchase price with an AIO, big fail for me. So because I went through DFS for this if I return it I have to wait 15 or so business days for them to get it cleared on their system. Then I have to reapply to make another purchase so lets add another week, then another 30 days for a computer to get here. Long story short, the Aurora R10 air cooled is not good at all. I need this computer so I will be keeping it but I will never buy Dell anything again after this. All they had to do was mail me an AIO and the VRAM heatsink after tech support agreed it was thermal throttling and not tell me they will put a new (same cooler with fresh thermal paste). I know how to build computers (not like it hard) and I understand computer related issues so being talked to like I knew nothing about computers was hair pulling. This was probably the most frustrating day I ever had calling multiple support numbers from, sales, tech support, customer support and DFS. Way to go Dell , you lost a customer by = - crediting me $150 on a machine I payed $450 more than on the website a week later - having horrible cooling on a machine that I have to take a house fan, open the case and blow air into it that way so I can game - not just fixing this issue by sending me the AIO and VRAM heatsinks (this would have solved all these issues and I wouldn't have cared about any of these other points) - trying to fix my computer with the same cooler and "fresh" thermal paste. Yes that is what is going to bring down my thermals. Maybe just maybe a couple C if you are lucky.
Aurora R10, R7-5800, temperatures