How do I access the settings of this page that appears after a customer has completed an order?

I just want to change 'My Purchases' to a link so they can go straight to that page, like how there is a link for 'Your Orders' just underneath

You can edit the language string in ACP. Search for "Thank you for your order", find the string in question and add a link to 'My Purchases' like:

<a href="https://example.com/clients/purchases/">My purchases</a>

 

Search for some part of this text in your language: ACP -> Customization-> Languages -> edit your language -> search and edit. Save. 

Thanks guys, it worked! 😄