This is largely a repeat of the previous answers but worded differently.
Question 1. “It is very hard to turn the knobs. It takes a lot of strength. What can I do make them easier to turn?”
This is not normal. It will be helpful if you examine the figures 1 and 2 in on page 3 of the manual (first link below) to specify which knobs are hard to turn. Use the nomenclature given in the list so that we all know which parts are involved. All knobs should all turn with relative ease.
See page 3 Figure 2 of the manual. It’s imperative that the Elevation Lock #18 in the photo be UNLOCKED before attempting to raise or lower the carriage on the column.
http://www.jollinger.com/photo/cam-coll/manuals/enlargers/beseler/Beseler_23C(newer).pdf
Question 2. “The glue the attached the upper bellows has old and the bellows has detached. What can I use to attach the bellows and make it light proof?”
A photo would help us understand the problem. I think that the glue is probably some type of rubber cement.
Question 3. “In moving the enlargers, I took the condensers out so that they would become damaged (one is damaged). How do I clean the lenses?”
This is a common task with the Beseler 23 C enlargers. Remove the condenser unit from the enlarger. The safest workplace is to sit on a bed so that a condenser lens can’t drop to the floor (bad for the floor, worse for the lens). use the appropriate Phillips screwdriver to remove the screws. Remove the lenses and clean them with Windex or other glass cleaner, reassemble.
Be careful. The screws are tapered sheet metal screws fitting into a shallow cross section of aluminum. Tighten just enough to secure the condenser in position, so as not to strip the cylindrical housing. Be carful to not lose the clips.
Use the manual to refer to the parts you wish to remove. Those that aren’t well covered in the manual can be described to the best of your ability with reference to their position to the named parts. One of us should be able to figure out what you need and how to deal with it.
Many components of these enlargers can be found on eBay if necessary.
The focusing knobs get hard to turn due to excess friction between the plastic lens stage bushings and the two vertical guide rods. What usually happens is that over the span of many years, the rods acquire many little knicks and dents. That slightly increases their OD and generates excess friction.
You can polish the rods with medium or coarse steel wool to remove the high spots on the rods. This can significantly reduce the friction in raising and lowering the focusing stage. Don’t attempt to lubricate the rods.
Focusing requires the friction of the steel wheels on the focus shaft to drive against the guide rods. Lubricant on the rods would defeat the necessary friction. After polishing the rods, use a vacuum cleaner to remove all steel wool strands from around the rods and the bushings. Don't use sandpaper. That would roughen the rods and increase the friction.
Here’s a second version of the manual.
http://www.jollinger.com/photo/cam-coll/manuals/enlargers/beseler/Beseler_23C_II.pdf