@Galate,
Welcome to HP Forums, this is a great place to get support, find answers and tips.
Thank you for posting your query, I'll be more than glad to help you.
I understand that you are unable to scan from your HP DeskJet 3755 All-in-One Printer to your Ipad.
This issue could occur if the correct drivers are not installed or configured.
Let's go through a few steps to resolve this issue.
And here's the step by step guide for you in the link to install the HP AiO Printer Remote App from the link: Print and Scan from the HP AiO Printer Remote App (Android & Apple)
Let me know how this works.
You have a good day ahead.
Rainbow23 - HP Support.