Since you didn't provide the actual chemical compound of interest, here is an example and you can apply the same reasoning/calculations to your specific example.
Compound x has a molar mass of 123 g/mole. This is equivalent to 123 mg/mmole and 123 ug/umole.
If you have 1 umole of compound x, and you want to convert this to mg of compound x, then...
1 umole x 123 ug/umole x 0.001 mg/ug = 0.123 mg