Furnace Ideas / Help

LOL I mis-understood. For some reason I thought you wanted it sped up. It is LIKELY already on low for the furnace, that is if you don't have the green/ AC mode activated. Back in the day we had a couple we had to install minimal duct AKA louvered inlet air / filter mount and a plenum box with maybe three outlets just to provide a bid of restriction.

In some cases (it is not recommended) but you may be able to over-fire the burner to get the air output a bit warmer. You want to check this tho, with the indoor temp up to at least 65F or so