You need to take the extruder out first. Then you can see the side view of the extruder.
There is a small hole under the hose connector, there is hex nuts inside, align with the hose connector and screw it.
Before you take the extruder out, google for procedure or youtube video on how to take jr. apart and how to re-assemble it. If you are not confident yet, don't start, you are likely unable to mount it back or break the plastic fitting on the side panel.
(Da Vinci 1.0, Jr. 1.0 RAMPS, miniMaker) X4, (Creality CR-10S, CR-10 mini, Ender-3) X4, Anycubic MEGA X4, Anycubic Chrion X1, ADMILAB Gantry X2 (MonoPrice Maker Select V2, Plus, Ultimate)X4--Select mini X1, Anycubic photon X4, Wanhao duplicate D7 X1.
iNSTONE Inventor Pro X2, CTC Dual X2, ANET-A8, Hictop 3DP-11, Solidoodle Press, FLSUN I3 2017X1