I'm not saying you should open the case, but considering the shortages of PC parts happening right now, you probably wouldn't be getting warranty service in any timely manner if they would even "fix" the issue by replacing the thermal paste or the entire cooler. I don't know how true the rumors, but I've been read and hearing about people having their prebuilt systems or GPUs being fully refunded instead of repaired or replaced because new parts are just not available.
I personally wouldn't worry about the warranty when opening the system, because as long as you don't destroy your GPU, you shouldn't have too much problem replacing the other parts yourself if you somehow managed to destroy something. Repasting the CPU is very easy to do and may not even void your warranty assuming you don't change the heat-sink out and then try to get warranty service without putting the original cooler back.
You could just replace the cooler with a better tower cooler that uses the original mountings on the motherboard. As an example, there is this 92mm fan tower cooler that should fit in your case.
https://www.newegg.com/rosewill-rocc-16003/p/N82E16835200114