gear and shift levers have to be bought, bar diameter of flat bars is less [7/8"] than the tubing used to form
all those curves of a drop bar, assuming that is what you call curve bars ..

7.3 Trek Hybrid. means you got one with 'straight bars'


Given many upright type bars, have curves in them , like on A 3 speed , a beach cruiser and so forth..

and to function the levers are different so, shape is different. brake cables ends are different too,
that is why taking everything, off , as a whole .. is suggested .. stem type and bar clamp opening changes too..

Loosen the 4 bolts at the far end of the cable, at the shifters and brake levers, pull them out .

loosen the stem from the fork, and start over with all new parts ..

bars stem cables housing grips and levers..

essentially converting a roadie, to a hybrid bike.. in some markets
A road bike Hybrid, with Narrow tires gets called a Fitness Bike ..

for European markets Campag and Shimano made Flat bar Brifters to work
with Road sized chainrings.. and Front derailleurs.