How do I get a big clump of melted PLA off my hotend without wrecking it?

The short answer is to replace the hotend if the wires are compromised, but if they look okay, using a heat gun on a very low setting while gently peeling the plastic away is the standard procedure for getting the stuff off.

Trying to yank the solidified plastic away is a bad idea because it'll inevitably stress those wires, and since they are thin, they can just snap or pull loose from the solder joint. If you get the wires frayed or cut, you're looking at a completley new assembly anyway because the heat block is fused to the wires. If you go with the heat gun approach, use it from a distance and keep the heat focused only on the plastic, not the actual copper wiring. You want to soften the polymer so it starts to peel away from the heat sink and the wires rather than tearing. The goal is to break the bond between the plastic and the metal components.

If the nozzle looks off-center and the plastic is jammed around the heating element, you probly want to replace the entire assembly. Most kits on Amazon are inexpensive and much easier than trying to surgically remove the hardened material and untangle the mess. Since the plastic is alredy adhered to the block, it's probably already compromised internally. Ultimately, unless you are comfortable stripping the insulation and re-soldering tiny wires, swapping the whole hotend is the cleaner fix. It'll solve the blob problem, and it'll ensure the pressure isn't bent in the nozzle itself.

Seconding the swap-the-whole-assembly route. I had a similar blob situation on my printer last year and tried to save the stock hotend by picking at it with the bed heated. Got 90% off, but the print quality was never right after because the nozzle had been knocked slightly crooked, and I wasted two weeks chasing bad first layers before I gave in and replaced it. New one printed perfect on the first try. Also unplug the printer before you're working that close to the wiring, just makes it easier to not think about it.

Once you've got the new one on, worth figuring out why it let go in the first place. I had the same thing happen on my old printer and it turned out my Z offset was a hair too high, so the first layers weren't squishing down properly. Washed the plate with dish soap and dialed the offset in and haven't had a release since. Two weeks in you might still be tuning that stuff, so don't beat yourself up over it.

Been pulling blobs off hotends since my old Anet days, and the trick nobody thinks of is removing the whole thing from the printer first. Unbolt it, hold it with a pair of pliers, heat it with a torch lighter and the plastic picks off with a toothbrush or wooden skewer in about ten minutes. Way easier than fighting it mounted with wires hanging everywhere. On the off-center look, don't assume the blob bent anything. On the Neptune the whole print head can get shoved sideways when a print crashes, so loosen the belts, square the gantry back up, and run the auto level. If it still sits crooked after that, then yeah, swap the hotend.

When I cooked a hotend the same way years back, the thing that saved my sanity was a cheap silicone sock for the heater block. Didn't fix the mess, but once I had the new one installed I slipped one on and in three years since I haven't had a single blob weld itself to the block. Comes off in seconds when plastic does build up. Not saying it would have saved your old one, but for a bigger bed printer where prints run long, it's cheap insurance while you're still dialing things in. Check the wire insulation on yours closely under good light before deciding to keep it.

So I decided to try removing the whole hotend assembly first like one person suggested. I heated the area with a torch and the fused plastic started lifting right off using a scrub brush. It was much less of a struggle than trying to peel it while it was still in place on the build surface.