Your best bet is to e-mail him, contact him on Twitter or some other method.
RobTop, at the best of times, is not going to be active on Newgrounds. Newgrounds are not the people to contact. So, us mods are not the people to contact. In response to all the thefts and an immense reaction on Newgrounds against GD-related theft, and the temporary takedown of Geometry Dash from Steam, RobTop not only overhauled the submission system so that those who were here before 2013(?) have automatic submission rights anyone in future who wanted their music to feature in GD had to be whitelisted by RobTop himself. Seriously, this has been a year and a bit now since this has happened, I don't know WHY people are not getting the fucking memo by now.
The most important thing is that you need to contact RobTop yourself.