Hi Nishant,
It is not making measure column to USD but appending currency column(USD in your case) to measure, which can be done as below
-> click on measure at semantics
-> go to Properties tab and choose 'Amount with Currency Code' property Semantic Type
-> Type 'USD' at Currency column as shown previous reply(or choose value from TCUR schema as Anindya said)
-. click ok, activate and check your data preview
Regards,
Shireesha