On the Wonderswan Color, the new C14 is slightly larger circumference than the one being replaced. It’s also very close to the cartridge socket. We recommend that you add solder to the PCB pad closest to the cartridge socket and, while still applying heat to keep the solder molten, you slide the capacitor into place. Then solder the other leg/pad.
On the SwanCrystal, C15 has a similar issue, but it is further away from the cartridge socket, so it’s not as tricky.