@SplotchyAphid05
I'm uncertain whether your gear is in the auto or sitting on the floor but I start with the top 2 bolts, then work my way down.
If you are trying to do this in the auto, I recommend getting a transmission jack. They can be adjusted in 2 or 3 planes...meaning I can adjust the angle it is sitting to ensure that the engine and transmission mating faces are parallel to each other; this lets the alignment dowles slide in more easily.
You could also dab a little petroleum jelly or grease on the alignment dowels to get the party started.
If you aren't in the vehicle, then use whatever you have available to get the front of the transmission and the rear of the engine mating surfaces parallel to each other; then all you will need is for each to be at the correct heights, to align the dowels. Again, if on the floor, I start with the top 2 bolts (finger tight) then work my way down. Once they are all in I will tighten them hand wrench tight (just snugged up), then do a final tightening with the appropriate torque wrench.
It will also help if whatever is supporting the components is on wheels, so that one person can slide them about with little effort. It may help to get a third hand in there if your still experiencing difficulty.