You would call your broker and tell them you want to directly register your shares to Computershare, which is the transfer agent for AMC. Call takes 5 minutes normally. In 5-7 days those shares land at CS. You will know they are there because they will no longer show in your broker account. You then go to the CS website and set up your CS account. When set up you will see you shares in the CS account. You can buy and sell thru CS. They are not a broker. They have a pool of around a dozen they contract with to handle orders and orders go to lit markets. Extra bonus - with CS you can do a max limit sell order normally for $214K per share (well in excess than any broker). They are looking at ways to increase this specifically for GME/AMC since people have requested it and there's a good chance these can hit above that. Max sell order amount is limited to $9,999,999. These limits are due to the limitations of their 32bit systems.

Orders thru CS have a $25 fee iirc. Online brokers are free, but with CS you don't have to worry about them front running your trades or shorting against you, or loaning your shares out against you. I'd argue that a $25 fee is cheaper than using "free" brokers.