Go to the Translations section in your store's Admin area (Store setup > Translations).

In the list of your store's languages, locate English (or the name of your store's default language) and click on it.

You will see the Edit labels page allowing you to access the text labels of the language you have selected. Alternatively, you can open the Edit labels tab directly and find the required language there.

Use the label filter to find the text label responsible for displaying the text you want to change: copy and paste the phrase "To contact us, please use the form below" into the Enter search pattern field and click Search.

X-Cart will search for the labels of the selected language. Locate the required one in the label list below.

Click on the label name to expand a text area containing the current label value.

Edit the label value as you require and click Save changes.

Check the results on the storefront.