A specialized flashing kit or an MBus/FBus data cable connected to the test points located under the battery compartment. Standard Software Tools:
If you are looking for simpler software fixes without a full flash: Default Security Code Soft Reset to restore factory settings and wipe data. Check Version on the home screen to see your current firmware version. For those repairing hardware alongside software, detailed NHM-5 Schematics can assist with circuit-level troubleshooting. specific version of the NHM-5 firmware, or do you need help setting up the physical connection for flashing? Security settings - Nokia 3310 3G User Guide - HMD