[Question] How do I shorten straps on a dress that are Sewing Machines Parts and Sales in Los Angeles

I’m trying to make a dress fit me better, and to do so I need to shorten the straps. The problem is, the dress seems to be poorly made, and when I shorten one of of the straps, the widths come out to be even (same size widths, easy to sew), but the other strap seems to be two different widths, and no matter where I put the middle seam (?), I can’t get them to be the same width. I’m kind of new to reddit, so I’m not sure how to post pictures on posts like these, but basically one strap is very simple to sew and the other is difficult. The straps are standard & not lined, and the dress is 100% cotton and doesn’t stretch much at all. I’m a novice sewer, and I don’t really want to rip out the side seams on the strap (not sure if that’s what they’re called) to make it thinner, but I don’t see another alternative. Does anyone have any suggestions on how I should do this, or maybe a link to a website that would help explain what I should do? I’ve looked everywhere, but I can’t seem to find anything. Thanks in advance!