Depends on what the code is. If it is a Javascript or html code, to load it in Soho, you need to insert a Custom HTML object in your page and insert the code in it. You will need to first save the code as file and them upload it before you can insert it in the Custom Code object.

Since you are talking about a Thank you page, i suppose that this is a Newsletter signup or something similar. In this case, you should add such a page in your site (but not in your menu) and set this page to be the return (thankyou) page.

In this case, the code should createa Sign up form in your page. So you need to place the Custom Code object wherever you want this form to appear in your page.
To insert code in this thank you page, you do it excactly as you do for the index (home) page through a Custom Code object.

Read the instructions that come with your code.

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