simplewallet has a --generate-from-keys option for this.
./simplewallet --generate-from-keys newwalletname
You will asked to supply the keys, which I believe you get get from mymonero.
how to use spendkey
chenqi1112 posted this 8 years ago
https://mymonero.com/ seed is 13 words. but simplewallet is 25 words. than how to use spendkey import another wallet