Belly button closing up after revision. What can I do? (Photo)

I am sorry to hear that you are having problems with your belly button after your tummy tuck.  This is a relatively uncommon issue, but it sounds like your surgeon has done everything correct in managing the issue so far.  Although uncommon, a second revision is definitely a possibility.  Wearing the ear plug will likely be necessary again and your surgeon may even suggest steroid injections to help calm down the "over-active" scar tissue in that area.Best of luck with the second revision!

Idea with earplug is good; you just have to continue that for at least 6-8 months until scar is more mature, even longer (overnight). BB revision should include at least one small flap to brake a circumferential scar to avoid recurrent scar contractures.  

Your belly button problem is more common than most realize.  It is typically caused by an occurrence known a cicatricial scarring, where the scar contracts in a circular manner and the forces pull the surrounding tissue inwardly.  I am sorry to hear that you are having this issue.  Fortunately, your surgeon is attentive and is willing to take care of your problem.   It is likely that you will need an additional revision but I would recommend allowing the scar to fully mature first.  Scar maturity may take up to one year.  In the meantime, steroid injection with or without 5-FU may be attempted to halt or stop the aggressive scarring.  
In the event of a revision it will be important that the scar is not simply excised and closed again in a similar circular fashion.  An intervening flap of skin interposed into the belly button can serve to break up the contracting forces in the new scar.  I know this can be disheartening but I predict a successful outcome if you exercise patience, have a positive attitude, and continue work with your surgeon. 
Best of Luck!

Dr. Jones