missing inputs error can mean two things: the parent transactions do not exist anymore OR the outputs that your transaction is trying to spend are already spent by another transaction.
You can first try looking up the txids of the inputs for your transaction in a block explorer. Those txids are the parent transactions, and if you see the transactions in a block explorer, check to see whether the outputs you are trying to spend are already spent. If they are, then your transaction is actually a double spend and is invalid. There is no way to make it valid nor is there any way to "retrieve the coins" from it.
If you see that the outputs your transaction is trying to spend from are still unspent, or if the transaction that spends them has the same transaction ID as your transaction, then that means that your wallet is not fully synced yet.
If you do not see any of the parent transactions, then there is nothing that you can do. It is impossible to determine the contents of the parent transaction given just its hash. You would need to have the full transaction of each parent transaction, but if you do not have those, then there is nothing that you can do.