Your question is not clear as to whether you are interested in recovering a wallet or if you would like to write software implementing a mnemonic HD wallet.
If the latter is true, BIP 39 is the original proposal, explaining mnemonic recovery phrases as a seed for HD wallets, and references some examples in various languages to get you started. Chapter 5 of “Mastering Bitcoin” by Andreas Antonopoulos offers a detailed technical explanation of HD wallets and mnemonic recovery phrases.
As for recovering a wallet from a mnemonic phrase, many popular cryptocurrency wallets offer this option, and can be found through an Internet search (I can not recommend any and would advise you to do your own research on which best suits your needs).