It is Legal and there are many wallets and exchanges giving the option to trade your funds on their bot. For Example Magnum has a auto trading option. Magnum is a wallet and it enables the bot through API and you can monitor it through telegram app. There are more such facilities.It is not important whether the facility of bot is available or not.

The important thing is

• To know the PnL ratio of the BOT.
• If there is no such previous data available then test it with very small amount or try it on testnet.
• Even after all of this please make sure that the bot is placing proper stop loss so that even if the market goes against the order set then you face minimal loss and are not liquidated.
• If the bot is not setting stop loss then you set manually by logging in to your account.

   
 
Note: I am not here to promote magnum thing, please do your research before using it.