Kukkorose no Himekishi to Nari, Yuri Shoukan de Hataraku Koto ni Narimashita.

Talk about your extreme career changes! Naruse Soushi, a middle-aged man and private secretary to a politician, lies on the verge of death. Meanwhile, in another world, the princess knight Reina has been captured by an enemy nation. The princess' soul is removed–and Naruse is summoned into the empty husk of her body! Now that he's taken over the form of this beautiful young woman, he's doomed to her fate: being sold to a yuri brothel where he has to service female customers. He's determined to learn more about Reina's life before he took it over...while he finds a way to work the grind in her body!

(Source: Seven Seas Entertainment)