It sounds like you're asking for the plot of Doraemon Season 17, Episode 44. However, please note that episode numbering varies significantly between different versions of the anime (e.g., 1979 series, 2005 series, and regional broadcasts like USA or India).
After a muddy chase through underground pipes, Nobita gets the crow to cough up the key by offering it a piece of candy from Doraemon's pocket. Gian, impressed by Nobita's determination, calls off practice. doraemon season 17 episode 44
Desperate, Nobita uses the Small Light to shrink himself and search the sewer. Inside, he encounters a lost baby crow who has swallowed the key, thinking it was a shiny pebble. Nobita befriends the crow, but Gian and Suneo — also shrunk — chase him, thinking Nobita is faking the crisis to avoid practice. It sounds like you're asking for the plot