Not a sensible thing to do unless you have all the details, at best it will be a millivoltmeter and you will need multipliers.

If you pick the wrong beast such as a moving iron you would come badly unstuck.

Though, if you get one with a shunt and a Darsnoval movement it is possible,

A good current meter, with a low value shunt, may have a 1 milliamp meter.

I have done that many times by just adding a switch (DPDT) = Double Pole Double Throw, and adding the necessary resistance for the voltage reading which most of the time is 1 Kilohm per volt of display, less the internal resistance of the meter for the first 1 volt reading.
Vane type current meters DO have a high internal current which make them BAD for voltage reading, though in some cases, the say arrangement with the caveat of about 10 to 50 milliamps meter, so in those cases I have used a momentary switch to make sure that the switch is returned to its original setting of current meter position.

Some vane meters are very high current, equal to the current peak reading capability, so not possible to convert to a voltmeter.
Some, like in the cars or automobiles, have a thermal movement, this to avoid the car vibrations.