I know the House of Commons website has the text of bills, but this is an amendment to a statement, so I can't for the life of me find it; any help much appreciated! :)
It's not actually all that illuminating, but you can find the actual text of the amendment in the House of Commons order paper for the 29th January 2019 (see page 21)
At end, add “and requires the Northern Ireland backstop to be replaced with alternative arrangements to avoid a hard border; supports leaving the European Union with a deal and would therefore support the Withdrawal Agreement subject to this change.”.
This needs to be understood in the context of the original motion from the Prime Minister
That this House, in accordance with the provisions of section 13(6)(a) and 13(11)(b)(i) and 13(13)(b) of the European Union (Withdrawal) Act 2018, has considered the Written Statement titled "Statement under Section 13(4) of the European Union (Withdrawal) Act 2018" and made on 21 January 2019, and the Written Statement titled "Statement under Section 13(11)(a) of the European Union (Withdrawal) Act 2018" and made on 24 January 2019.
You can also find the Hansard record of the debate, which has the text in a somewhat harder to read format. More generally, if you know the day something happened, this page is a useful resource. Note that in spite of the wording, this isn't actually a commitment for the House to do anything.