I would contact Daisy Customer service and ask for a parts diagram. See the link below.
I suggest you search the web for "Air gun repair" and locate someone near you to repair the rifle. See the link below.
To fix a Benjamin air rifle 397, first ensure it's unloaded and safe to handle. Common issues often involve the seals or the pump mechanism, so disassemble the rifle carefully using the correct tools. Inspect and replace any worn seals or O-rings, lubricate moving parts with appropriate oil, and reassemble the rifle. If problems persist, consult the manufacturer’s manual or seek professional repair assistance.
I just bought one at a garage sale (same make and model) but the "plunger" is broken. If you get a source of parts let me know Answer All of the "Cactus Carbines" were made for Sears by Daisy. Any reputable Daisy repairman can fix you up.
Unfortunately this rifle is not worth repairing. In Excellent condition it is worth $18. It has an FPS of 250 FPS. That's slower than a Daisy Red Ryder. I really suggest you purchase a new air rifle. These air guns were not designed to be repaired. Marksman is owned by Beeman. If you want to try I suggest you call Marksman at 800-822-8005
Use a pump to pump it up.
You replace it you do not fix it.
Replace the water pump.
It depends on the model and what is wrong with it.
how do i fix leaking spray pump on a 2 barrel carburetor
In the good old days you could fix a fuel pump with a rebuild kit. These days you can't fix a fuel pump, you replace it with a new one.
Do not attempt to "fix" ammunition. Dispose of it properly. Ask your local police for help.
It all depends on what is wrong with it.