"the bearings are already/still in the frame right? most important when mounting the fork is that the bearing seats on the fork are perfectly clean. not scratches, no marring and no loctite remnants. you may want to carefully clean the with fine sand paper. same with the inner side of the bearings.
if helps if you put the fork into the freezer if it is large enough and wife allows take it out, wipe the bearing seats dry, apply a thin layer of loctite to the bearing seats and carefully "hammer" the fork into the bearings.
don't hammer on the drop outs and don't hammer on the underside of the crown directly but use a round piece of wood that snuggly fits into the underside of the crown, wrap it in cloth and hammer on that piece of wood. you may replace the wood with something else that is fit for purpose.
don't hammer hard but use a hammer that is heavy enough. if the fork doesn't slide in easily something is wrong. the press fit is not overly tight and if the fork is cooled down it should be slim enough to slide in relatively easily.
IMPORTANT: mount the bottom seal before you insert the fork!