Hard lump under lip from being split open, what can I do? (Photo)

It appears that you have a left upper red lip scar. I would try steroid injections first and if no improvement after two injections, spaced two months apart, I would offer you a surgical lip scar revision. This has to be done carefully by an experienced lip surgeon.Consult with an experienced lip surgeon for a complete range of options that are appropriate for your situation.
Gary Linkov, MD
Lip Specialist / RealSelf Lip Lift Medical Reviewer
Manhattan

While this is rather common, most patience do not come in for this complaint. In the general scheme of things, there is still changes that will go on in the tissue over time. There may be some modalities like vigorous massage or steroidal injections that may break up any dense scar tissue. My recommendation would be the former and to let time heal your issue. You can always see a physician to better understand your concern with a physical exam. 
Best Dr. B 

The development of scar in any type of lip injury/laceration is common. Over time it does tend to lessen but in some people may never go away. Because the lip is an area we constantly feel, such lip scar lumps can be irritating. The only way to resolve it is by excising the lip scar an replacing it with a small fat graft.

Hi there,Have a consultation with a certified physician and discuss scar revision and then possible fat grating or filler post revision.Best of luck...