Switching plans for 80 year old with stage 2/3 cancer?

tl;dr – 80 year old with cancer currently has a shitty HMO + Medicare and is receiving treatment too slow. How do we fix this?

I have a huge gap in knowledge when it comes to healthcare and I’m really hoping for advice.

I’m close with an 80 year old person in California who has stage 2 or 3 lung cancer–diagnosed over a year ago. Went into remission and now having tests done because mass seems to have grown.

They have Medicare and an HMO. The whole consultation/testing/analysis process is a nightmare of “hurry up and wait” where it seems like we’re constantly waiting for approvals to move to the next step in the process. In the meantime, months seem to go by and it’s hard to stomach possibly missing avoidable problems because too much time has lapsed.

Is there a better plan that should be purchased so that they can get tests and treatment faster? Are there health insurance consultants, etc. that I can call that will help us get set up with the best healthcare coverage for them?

Family members are prepared to assist with payment but I have no idea how to go about this or what it’ll cost.

Thanks very much in advance.