The curse of the Melo tanks.. great tanks is every way EXCEPT to open for the coil switching. The Melo2 is just as bad. I've sent Eleaf a few messages about it, but the Melo3 came out and I saw that they still didn't get it.
Where you need to hold the tank is by the glass and the metal part right against it at the bottom, not the bottom edge, you'll just unscrew the airflow section, while the top, you'll just unscrew the top fill cap.
Get yourself those tweezers with tank grabbing handle (like RedRebel posted above) maybe even two...they really work most of the time... someone needs to make better ones with a silicone or rubber insert for even better grip as they can slide a bit.
One very handy thing is:rubber tape (no glue, just stretches and melts with itself type) and cut a piece and use that for extra grip. Can be found in most dollar stores in the hardware area.
But just about anything to provide you that extra grip, rubber gloves as others mentioned, even tissue can help (a lot of time, it slips due to oils and liquid).