Clean it with a soft brush and a good multi-purpose cleaner. I spoke with Dicor on another matter and I also asked if my farorite Simple Green was ok to use as a roof cleaner. They said yes, I buy it by the gallon concentrate and dilute it for the job at hand.
Be sure to rinse it well and let dry completely. I would clean all of the lap sealer up close with the brush, you may have other joints that should be touched up.
If you do find the need to remove the old lap sealant, you can warm it up with a hair dryer or in my case I have a heat gun that a deflector that directs the heat across the sealant not at it. Be very very careful if you do use heat though, you could over do it in seconds.
What ever you do do not use anything with CITRIS or PETROLEUM distillates in it, it will ruin your roof faster than your can say I ruined my roof. You might not be able to see the damage immediately but the damage is there.