If you can't push it tight enough by hand to relieve the pressure, you can very carefully use a pair of large pliers like Channellocks and with the tip covered, squeeze it down with one jaw of the pliers on the tip and the other jaw further down on the fitting and relive the pressure. Make sure its covered with several layers of a shop towel or strong cloth as there is a lot of pressure and will spray fluid everywhere. Just don't bend the tip on the fitting which isn't easy to do. Once you release the pressure, the fitting will slide right in.................