Get your taxes done using TurboTax

How did you transfer it?  Did you transfer the actual shares or did you do a sell from Robinhood and then a buy at webull?  No the IRS might not know your cost.  Webull might not even know your cost.  So you will have to enter each sale and enter the cost to figure the gain or loss on each sale.  You are only taxed on the gain, not the total proceeds.