I can't import my investment from Robinhood because the transactions are over 1500. What should I do to report my capital gain/loss (if not input by manual). Thanks?

Since you cannot upload this many transactions into TurboTax, you can enter the summary of your transactions as grouped by sales category.  You can select that you are entering the summary instead of individual transactions.

Please see the following for more detailed instructions:

Entering summary transactions