Hi, dear yasin
if you refer to AMC1 ORO.GEN.205 you will find your answer. In addition, GM1 ORO.GEN.205 have been given you some examples. So as it mentioned in ORO GEN.205 any parts of operator’s activity must be conteracted.
Best Regard

For Commercial Operators (other than Licensed Air Carrier), a Part CAMO or CAO is mandatory. Saying so, the maintenance agreement depends of who performs maintenance and can be covered by either Part CAMO (check Appendix IV to AMC1 CAMO.A.315(c) — Contracted maintenance), Part M or Part ML. Depends on the type of aircraft and type of operation.

As João alludes to, it is the CAMO approval directly linked to the AOC approval (see any AOC certificate and Ops Specs for reference to CAMO approval number) that controls and arranges maintenance contracts, not the AOC operator directly. This is why the AOC will have a nominated person for continuing airworthiness, to oversee such work.