Fontlab doesn't magically

In reply to CHANGING FONT WEIGHT IN FONTLAB:

Fontlab doesn't magically make your font bolder or lighter.
You have an effect that does that, but it's gonna be far from good. You will have to draw after that, correct it.

For MultipleMaster to work, you need 2 weights with similar outlines in terms of amounts of points and starting points.

But if it's from an illustrator moonoline, the easiest is to make it bolder in illustrator, then reimport it in fontlab.
After that you could try to mix both weights in a Multiplemaster to interpolate or extrapolate it.