quick run through on how too?
Assuming you already figured out which helicoil you need (UNF 3/8 24tpi, 3D (lenght) correct me if I'm wrong, going of memory here), if you wanna do a proper job you would also need the helicoil instalation kit. G mentioned you don't necessarily need the kit, and I'm inclined to blindly believe anything he says, but to me it seemed like a hassle without the right tools (although I bet G could Macgyver one in with a toothpick and a nice mug of tea). This kit is quite expensive, cheapest was like $20 or so, which back then equaled the price of a new axle, but seeing as Marmoset axles are near impossible to find since the Simians release I guess that's now irrelevant. Then for the actual instalation there's plenty of youtube how to videos, should be a pretty straight forward job. Make sure to use bolts with non damaged threads to avoid the helicoil from coming out again, and goodluck!