Did you get 3 1099B forms? Or 3 sales on 1 form? What kind of 1099 do you have? Did you get a consolidated statement. That will have sections for 1099-Int and 1099-Div and 1099B. You need to enter each section in the right place. So read it carefully and look for headings.... 1099-INT for interest or 1099-DIV for Dividends or 1099B for sales.
Are you trying to import the brokerage 1099 or manually enter it? I only know how in the Desktop program, not the Online version. They did change the way you enter 1099 forms this year. Maybe this will help.
Enter a 1099 B under
Federal Taxes on left or Personal (Home & Business)
Wages & Income (Personal Income)
Then scroll down to Investment Income
Then Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B) - click Start
Then click +Add Investments at the bottom
Then Import your info OR Skip Import at the bottom
Then pick box Stocks, Bonds, Mutual Funds - then Continue
Enter the bank or broker
Answer some general questions and Continue
Then Continue a couple more screens and you finally get to the 1099B entry screen.