You need to check the door springs. There is more than one type of spring but typically they are directly above the door or there is one on each side of the door. Make sure they are not broken. If it is the type above the door you may have to look closely. If the springs are in good shape go to the back of your opener where all those white wires go and you will find a couple controls. The one you want is the 'up force'. Turn it about 1/4 turn and try. Increase if necessary. Do not adjust the 'down force' as that affects the safety system. That "technician" is scary!