How can I help you? = HOW me-HELP-you?
Notes:
The sign "HELP" can include information about the subject and the object of the sentence. By starting the sign closer to yourself and moving it closer to the person you are intending to help you can indicate "I help you." Sometimes I type this as "me-HELP-you." When you use the direction of a verb sign to indicate the subject and/or object you are using what is sometimes called an "agreement verb," a "directional sign," or a sign that has the characteristic of "directionality."
There are several other ways you could express the concept of "How can I help you?"
For example you could sign:"I what-DO me-HELP-you ?" [lowered eyebrows the whole sentence]
or
"me-HELP-YOU? What-DO me?" [raised eyebrows, then lowered]
Notes: