In Coinbase, or any wallet for that matter, how do I reinvest profits back to more bitcoin/altcoin?
Cryptocurrencies don't have profits (because they don't generate revenue). I think you're referring to your investment gains, yes?
In Coinbase, or any wallet for that matter, how do I reinvest profits back to more bitcoin/altcoin?
In Coinbase you transfer Bitcoin, Litecoin, or Ethereum to your fiat based wallet (if you live in the US you'll have a USD wallet). Those funds sit in the fiat wallet until you're interested in buying Bitcoin, Litecoin, or Ethereum again.