Sometimes the theme you are using isn't perfectly compatible leading to the header covering where customers enter their order number and email address. We have a quick fix for this.
First, go to the 'Setup' section of the app:
Scroll down to the 'Legacy Returns Center Customization'.
In this section, you will now need to upload a white image. An example can be found below.
Once you have uploaded just save and check if this has rectified the issue. You may need to experiment with the size of the white image to get to the alignment you would like to see.
Any queries please don't hesitate to get in contact.