A bicycle bottom bracket is a component that will wear out with use. When this happens, you can disassemble it, replace the damaged parts with new ones, and then continue to use the bike.
Take a bicycle wrench and grasp the pedal nut where it connects to the crank arm. Rotate the nut in the opposite direction from which the pedal rotates when driving forward. Remove the second pedal in the same way.
Remove the nuts holding the wedges. Use a hammer to knock them out. Wedges are disposable parts - after removal they must be replaced with new ones. This can be avoided only if they were knocked out extremely carefully. Remember which cranks and pedals are left and which are right (pedals usually have corresponding designations in Russian or English).
Now the connecting rods can be removed - access to the carriage will open. The nut holding it is located on the side opposite to the drive sprocket. To unscrew it, use a so-called carriage wrench - it is expensive, but will allow you to repair the bike more than once. If there is no such key, be sure to purchase it, or, as a last resort, attach the head of the nail to the slot of the nut and begin to apply very light blows to the tip so that the nut begins to rotate counterclockwise. This process will be slow, but in no case try to speed it up by increasing the force of the blows.
Remove the carriage and replace it with a different one. Make sure that the new unit is installed the same side as the old one. Screw on the nut first with your hand, and then, when the strength of your hand is not enough, with a wrench or, in extreme cases, using the above method, with the only difference that you will have to rotate it clockwise. Be careful not to rip the threads. Lubricate the new carriage. If the chain comes off, put it on.
Put on the cranks and secure them with wedges. Drive in the wedges, and when their threads appear on the opposite side, secure with nuts. Screw the pedals into the cranks.