You would first need to go to your Admin page,
Click Content on the left hand side and then click "View Pages" and find the page in which the Text appears,
Once you have the page edit open, click "Open this page in Blocklab" on the right hand side,
You will now be able to double click the Text block which allows you to edit the text inside,
Enter the text you want to show and then click Publish in the top right of the screen once it has saved.