iphone 3g bootloader 5.9 downgrade baseband from 6.15.00 to 5.13.4

Please help me, is there any way to downgrade my baseband 6.15.00 to 5.13.4 with bootloader 5.9. ive searched and done all the steps but still no luck. all the steps is for 5.8 bootloader. or is there any way to downgrade my bootloader?

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