If your current software version is <=1.2.2.34 
Instruction:
Boot the switch with firmware version 1.2.2.34
Upload jump code ECS4620_jump_V115.11.3.1.bix to the switch
Boot the switch with jump code
Delete Firmware V1.2.2.34
Upload firmware V1.2.2.39 or newer
Boot the switch with firmware V1.2.2.39 or newer
Delete Jump code.
 

Caution: ECS4620_jump_V115.11.3.1.bix does NOT support ECS4620-28F-2AC.

Jump code ECS4620_V118.10.30.1.bix is for ECS4620-28F-2AC (2018/10/30)