Best way to fix this bulge caused from tethering of underlying skin to membrane around the implant? 1 month po. (photo)

A bit of excess tissue in this spot is not an uncommon problem after mastectomy and implant reconstruction. There are several possibilities:-
1. The shape of an implant vs a breast. Breasts have a round base but they also have an axillary tail with is a triangular shaped extension of tissue that takes the breast up to the armpit. When you have a mastectomy this axillary tail breast tissue is removed and while the main bulk of the breast volume is filled by the implant which also has a round base the implant does not have a handy little extension up the side to fill this space. This means you now have relatively more skin than tissue in this spot causing the fold. Now it also looks like you have had an axillary dissection and this also involves removing tissue inside and leaving skin which can add to the problem. This problem can be addressed down the track with fat grafting but I wouldn't offer this until at least 6-12 months post op. 
2. Fluid collection after an axillary dissection. There can often be a collection of fluid, called a seroma, that occurs after an axillary dissection. the lymphatic system that drains this normal fluid that bathes your cells now cannot travel up the usual lymphatic channels to the lymph glands because they have been removed and so this fluid collects. If you touch this fold and its feels like there is some fluid underneath it then this may be the problem. your surgeon may aspirate it with a needle or advise you to sit tight and let the body slowly reabsorb it naturally.
3. Tethering of the skin to the underlying tissues. If this is indeed just a tethering problem then the good news is that at one month post surgery you still have  influence over it! If your doctor has confirmed that the problem is tethering then with some judicious and regular massage you can break down that very early scar and re-fashion the contour.
At only one month post surgery it is early days so at this stage its is probably  best for you just to focus on healing and maybe start a little gentle massage. Implants need a good 6-12 months to "settle in" and look the way they are going to look in the long term and so the appearance will change and hopefully slowly  improve  with time. 
Congratulations on getting to this stage of your treatment I am sure its been a long journey.
Kind regards,
Natasha

This is not an abnormal finding after breast reconstruction. It is formed from a combination of the the mastectomy flap and your native underlying soft tissue. At this point you are very early on and swelling is still present. Things you can do right now are stretch, massage and ultrasound to the area. After several weeks/months have gone by your PS can reevaluate and decide the next steps with the  possibilities being skin excision or liposuction. I hope this helps!

Dear capri31,I understand your concern and it is quite normal to be concerned about the outcome following a breast augmentation surgery. However, you are still in the very early stages of the healing process at 1 month  post op.Your will need to be patient at this moment and follow what your surgeon has instructed you to do post operatively.At the early stage of the healing process, the tissues around the implants are still swollen. Once the swelling subsides and the implants drop to their final position, you will be able to see the final result of your breast augmentation surgery.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery