The is no tutorial how to set Zephyr to new architecture ?
The process is documented in the architecture porting guide but it is not a tutorial... it is more a check list that tells you which bits of the code you need to go an read.
do you know what are the changes to fit Cortex A to Cortex M ?
From the porting guide I think you would need to do review almost everything that is listed. There may be a couple, such as PM where you end up making no changes, but you would need to review each and every one.