Here you can find the instructions on how to change the newsletter text block.
Navigate to your Magento root folder on your server. Then, go to the app\design\frontend\TemplateMonster\themeXXX\Magento_Newsletter\templates folder. (XXX — your theme number)
Open the subscribe.phtml file. Enter the text you want to display within the newsletter block (replacing the old one). Remember to save the file.
*The text displayed within the newsletter block (e.g. Sign Up for Our Newsletter; Enter your email address) will always be after the echo __(‘ code part.