For real calibration, you will need multiple voltages ranging from say 100 mV to 1000 V. Also AC voltages up to 600 V at several frequencies and standard resistors. Read through the performance verification or adjustment section of a Fluke service manual to get an idea what's involved. The old Fluke 87(-I), for example, requires DC voltages from 0 V to 1 kV at 0.035% accuracy, AC voltages from 0V to 1kV at 60 Hz to 20 kHz at ~0.2% accuracy, currents up to 10 A both DC and AC up to 1 kHz and resistors between 1 Ohm and 100 Mohm with ~0.06% accuracy. Unless you have a small cal lab at home (there are some people guilty of this on this forum), leaving the meter alone unless it's obviously out of spec is usually the best strategy. The
mini metrology lab series by Conrad Hoffman could give you an impression what's involved to derive multiple voltages from a single reference. But that would be limited to DC voltages.
If you just want to do a spot check, the voltage references sold by
Voltagestandard and
Geller Labs are a good choice. The advantage you get from buying a pre-made reference is that someone will have calibrated it with a high-precision DMM with traceable calibration to a much higher accuracy than offered by the IC manufacturer. The Voltagestandard DMMCheck (plus) would probably be suitable. But note this is only for checks: it's not sufficient for calibrating a serious DMM.
If you want to go the DIY route, then
this thread might be of interest. There are at least half a dozen other threads about voltage references on this forum (Google is quite good at searching eevblog.com), but the general trend is to try to make a stable reference and then use a DMM to figure out the value, as opposed to trying to buy an IC with a very good initial accuracy.