i have junk fitting that i put in the vice tight, very tight..
screw the good fitting on the one in the vice...tighten with wrench..
put oil on the hose inside, use a heat gun to heat the hose till plyable not too much but hot push onto fitting do not stop til all the way on.
extra heat if needed.
sfter a few time you will be able to tell how much heat.
good luck
joe