Understanding phase noise specification in signal analyzer
After making some calculations and comparing my answer with some examples, I've found that the conversion is

PN_RBW = 10 log(RBW) + PN_1Hz

where PN_RBW is the desired phase noise (at the desired RBW (in Hertz)), expressed in dBc; and PN_1Hz is the phase noise normalized to 1 Hz as it appears in the datasheet.