How can I fix my double bubble? Is a strap at all used for correcting a double bubble? (photo)

There are 2 possible causes of double bubble, sometimes occurring together: implant dropping below the bottom edge of the breast, and animation from dual plane submuscular placement. Straps are sometimes used to try and stabilize the fold and hold the implant up, but more often a surgical repair is done. This involves sutures in the scar capsule called a capsulorraphy. If you see the crease pull upward when you contract your pectoral muscle, then you have what is called animation. That cannot be corrected with capsulorraphy, and should be converted to the split muscle.

I agree with what my colleagues suggested below for surgical approaches. These tend to be larger procedures with discomfort from stitches placed near the ribs.
A simpler initial approach would be to do a fat transfer procedure to camouflage the double bubble. Fat grafts take well on breast implant capsules. It would be a 1-2 hour procedure under local anesthesia or light sedation to harvest fat and place it from the visible bubble edge to the current inframammary crease. After 3-6 months healing if the result is not satisfactory you could proceed to the capsule reconstruction procedures.

Thank you for your question.
I do see your concern.  Generally speaking, a "double bubble" is a cosmetically undesirable circumstance for patients with breast implants, which occurs when the breast fails to take on the shape of the implant, resulting in the appearance of a visible line showing a separation between the bottom edge of the implant and the bottom edge of the natural breast.  Sometimes, in situations like yours, the appearance of the breast improves over the course of the first several months; sometimes, additional surgery may be necessary to improve the outcome.In your case, if the double bubble occurs does not improve with time, revisionary breast surgery may be helpful;  in my practice, this is usually done by raising the inframammary fold using capsulorraphy techniques.  This type of repair involves a two layer, permanent suture repair (reconstructing the inframammary fold areas). This procedure serves to reconstruct the lower poles of the breasts and prevent migration of the breast implants too far inferiorly.Sometimes, depending on factors such as quality of skin along the lower breast poles, additional support provided by acellular dermal matrix or biosynthetic mesh may be very helpful. I have also found the use of acellular dermal matrix very helpful in cases where the skin/tissues are very thin and in cases of recurrent breast implant displacement. Best wishes.