What can I do about this thermal pad?
Are you using solder paste or just soldering by hand? 

First fill the vias with just enough solder that the holes are filled. You don't want solder above the surface of the holes. 

If using solder paste, add  paste on top of and in the space between the vias as well as the lead pads. 

If soldering by hand, add lots of flux on top of and between the vias. After soldering the leads to the pads, turn the board over and apply heat to the vias. The idea is to reflow the solder in the via holes onto the thermal pad.