Problems with feeding the filament into the bowden tube
What you are after is a small common mod called... filament guide (as your question title!).

The first one to pop up in my google search was this one: https://www.thingiverse.com/make:346736 which in turn is a make of this model: https://www.thingiverse.com/thing:2242903

Also, a couple of tricks that help on my printers (YMMV):


manually straighten the first few cm filament before inserting it into the extruder (e.g.: remove the natural bend that is there because the filament came off a round spool by bending it in the opposite direction)
when the filament is past the gears/cogs, while still keeping the cogs "open" (i.e.: not yet clamping the filament), twist/roll the filament between your finger.
sharpen the tip of your filament with a pencil sharpener.  This make so that the tip of it is at the very centre of the hole, rather than at its edge.