They need to win the Battle of Plassey, which can be done by stopping Bengali forces from betraying the Nawab. You then need to stop either the French or British EICs from having a second go. That means crippling both, or having the Nawab successfully play them off against each other. The latter is probably preferable in order to get technological learnings from Europeans.
As for industrialisation, they already have three things going for them: urban centres, basic textile manufacturing, and coal reserves. Steel-making existed elsewhere in India (although I'm not sure about Bengal itself) so that's something else that can be done without too much trouble. Steam power would need to either be discovered or imported from the UK. Perhaps get some EIC official to set something up on his own account and for the technology to be copied by locals.
Your biggest challenge is probably getting some form of limited rule, so that the Nawab doesn't simply extract all the riches from the emerging capitalist class. Perhaps you can set up some sort of Mughal resurgence, which weakens the power of the Nawabs without replacing them, and gives more power to the middle class in the power struggle. Alternatively, you can have an enlightened Nawab who realises Bengal is falling behind and pulls a Meiji.