I have no Coinbase but I assume it works like every other exchange with either a “send” or “withdraw” functionallity.
Open an account with BlockFi or Celsius click on “deposit” or “receive” and get your Litecoin address. Then go to Coinbase to withdraw/send your Litecoin and enter the destination address you got from BlockFi or Celsius (your Litecoin account there).
Best to test it first with a small amount like LTC 0.01