There are a few different ways that you can log into your IRS business account, depending on what type of account you have.
If you have an Online Services account, you can log in with your user ID and password. If you don't have an Online Services account, you can create one by registering on the IRS website.
If you have an Electronic Filing Identification Number (EFIN), you can log in with your EFIN and password. If you don't have an EFIN, you can apply for one by filing Form 8633 with the IRS.
If you have an Electronic Payment Provider (EPP) account, you can log in with your EPP login and password. If you don't have an EPP account, you can apply for one by contacting an authorized EPP provider.