How to decode a ByteCode contract on etherscan for exemple : https://etherscan.io/address/0x6b75d8af000000e20b7a7ddf000ba900b4009a80#code?
It is a pretty difficult task to decompile compiled bytecode. There are some compilers such as https://ethervm.io/decompile, but the code it will produce will in most cases be difficult to read.
That is due to the fact, that firstly variable names are artificially generated (as original names are not written in the bytecode) and secondly the contract produced will be structured differently than the original contract, as the decompiler can't always tell which commands were used.
You can perhaps try with the Etherscan decompiler: https://etherscan.io/bytecode-decompiler
But as Nal said, it maybe impossible to get the exact same code you compiled.