"Select Convert from V3 CONVERT TO V3. is this right?"
Your initial task indicated that you wanted to get an item of clothing that was made for V3 to fit a morphed version of V3. So the answer to this question is ... Yes

"press convert and then select none of the morphs that it offers in a pop up."
Why select none? The very reason to be doing this is to place a morph in the clothing that matches the V3 morph. Select the custom V3 morph. Then as an option select some-all-none of the other available "WW" morphs as you require.

"I just don't get it. the CONVERT TO doesn't specify my character."
Your "To" character if I'm understanding you correctly is V3 with a custom morph in it. You will have ... or should have... selected the morph in the paragraph above. Wardrobe Wizard 2 has all the information it needs to perform the task.

Does that clarify?