From your description, they sound like "egg beater" drills, like this:
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If so, tuck the rear handle in the crook of your arm. Study how the crank handle turns the chuck, and position it so that it's sticking out sideways, on the side such that pulling down will cause the chuck to run in reverse. With the hand on the arm where the drill is cradled, grip the chuck, holding it firmly. Check that you don't have clothing or skin where they could get caught in the teeth of the gears. With your free hand, grip the crank handle and pull down (strong, steady pull is best).
If the chuck slips in your hand, and if you've got one of those plastic sheets that people use to grab onto jar lids to open them, or a piece of the abrasive-covered window screen used in drywall sanders, or a thin Scotch-brite pad, or any such a thing that will increase your grip on the chuck, use it.
In future, if the drill bit slips in the chuck in use, you can use the same approach in reverse to tighten the chuck.
If you have a brace, like this,
you just grip the chuck and pull on the handle.
If you have a push drill, some version of this,
the collar on the chuck will either turn (right to tight, left to loose) or pull forward or back to release the bit.
But, if none of this describes your situation, pictures would help.