Take the rotor off and look inside, it’s usually held by a C clip or small bolt, then you should be able to solder new wire yourself, be sure to get solid head shrink over the joins and cover the copper windings to stop any spatter getting on there. Blutac is useful for that. You want a quality 18AWG silicone insulated hobby wire for most 30A peak motors, or 16AWG for larger ones.