Loose skin after liposuction. What can I do to tighten my arms? (Photo)

Hi and welcome to our forum!
From your photo, I note considerable skin sag of the upper arms associated with overlying stretch marks.
Stretch marks indicate the presence of permanently damaged overstretched skin usually occurring during pregnancy or significant weight fluctuation where when pregnant or heavy, the skin's dermal elastic fibers rupture, resulting in the loss of elasticity and the development of streaks on the skin surface. The skin will stretch over a greater surface area and will predispose to further sagging.
The extent of the sag precludes non-invasive techniques. A brachioplasty will be required. This involves an excision of an ellipse of excess redundant skin from armpit to elbow, placed on the inner aspect of the arm to minimize visible scarring.
Visit a board certified plastic surgeon for evaluation and discussion.
Best wishes...