I'd say you need to buy at least the MG34 manual D 124/1, or even better, the Butz manual about the MG34.
From D 124/1, page 22:
e ) Disassemble the bolt:
1. uncock the bolt by twisting the bolt head in the bolt housing and release the firing pin lever
2. disengage the firing pin detent of the firing pin nut and twist off the firing pin nut toward the left
3. remove the bolt head from the bolt housing
4. place the spring retainer with its flat sides in the hole with corresponding flats at the rear of the
bolt housing, and with counter-pressure against the firing pin, twist to release it from the locking
grooves of the bolt head
5. remove the firing pin and firing pin spring from the bolt head.
Considering the price of the gun, a manual is ridiculously cheap for what it contains.