If you are using a computer, do the following:
1. Set up your next move like you normally would.
2. Look below the 'submit' button.
You will see "Offer Draw", "Claim Draw", and 'Resign" buttons.
Click the "Claim Draw" button.
3. Next, submit your move as you normally do.
If the conditions are correct for claiming a draw, it will be declared a drawn game.
If conditions are not met, your claim will be ignored and the move will be played as entered.
If you are using a phone or other device, you will need to check the menu options on the game page to claim a draw.
I have not claimed a draw in this manner, but I believe this information is correct.
If not, I'm sure someone will provide a better answer to your question.