Did your brother file a 2018 or 2019 tax return with direct deposit information on it. If he did and the information is still correct, he does not need to do anything.
If he doesn't file a tax return and doesn't receive social security benefits, then he can use this web site to complete the information: https://turbotax.intuit.com/stimulus-check/
If he filed a 2018 or 2019 tax return and there is not direct deposit information on it or if the bank account has changed, he will need to enter his information on an IRS portal after it is put online sometime soon.