I found a way to increase the gap, press Enter in the end of the text to add a row, then press Space to make a blank row, then set the first row content without underline, the second blank row with underline and change the font height smaller.
I don't find a direct option to adjust the gap, in Microsoft Word, can raise the font position to increase the gap, but in Creo, I don't find that option. Another indirect way is to sketch a line and group them.
