Parge coating crumbling block/parged retaining wall

hey, i've got a block retaining wall that was parged a long time ago and it's crumbling on one side real bad. i was going to try and hire someone to fix this but was wondering if this might be a diy job for me and what would be involved? it's a tricky spot because it's on a corner that is rounded and has a unique shape kind of. thoughts?