It should change automatically after you buy the hoodie when talking to S'rami in MC's house after meeting Mirimiel.
When you exit the Underdark with the Amazon and the Dark Elf, you're supposed to sleep at the MC house, then S'rami is supposed to say in the house temporarily with a sleep event next to the MC's bed. As the Amazon you must find S'rami's cousin so she can joins the party then you can enter the clothing shop with and buy the required hoodie to disguise S'rami.