Slider text can’t be changed

My website is https://www.metaphorenglish.com and it’s running on the Optimizer theme. Recently, I’ve discovered a very irritating bug in Optimizer. I can’t change the text on the frontpage slider. I want to remove the line “Download the culture hacking book for free” on my frontpage. However, no matter how many times I delete it in the “Customize” menu, it just doesn’t seem to work. I press “Save and close” numerous times, but the line is not deleted. Could you help me please? It would be quite urgent.

Thank you for your support!