Contact your MP and ask them to vote for it. This is what I have sent to mine, who happens to be Labour's Brexit spokesperson, Sir Keir Starmer:
Dear Sir Keir,
I trust you and all Labour MPs will be supporting Yvette Cooper's amendment to help prevent a disastrous 'no deal' Brexit.
MPs are running out of places to hide, and those politicians and parties who do not make every effort to spare the UK the damage that Brexit will cause are likely to find themselves judged very harshly.
Yours sincerely and Happy New Year,