Okay!
I have a experience that I recover my old 4036 switch on u-boot console. There is seversl scripts.
Unfortunately I can'n remember exact command for 4036...:(
But I think there is self rebuild script to build a default boot environmrmt include firmware loading procedure. If you can connect serial concole, when a message that press any key to stop normal boot or etc, press any key then you will be on u-boot console. ? or help + enter shows u-boot command lists then you can try search command that I said above.
Good luck...:)