And,  at  least  in  my  case,  the   ID  and  psw  do  not  result  in  importing info from  my  current  account &  I  remain  logged  into  the  same  new  user  account.    Any  suggestions?

When you go to your profile on your main account, click on the info tab. There you see your player ID.

Now when you are logged in on yourr new user account on mobile also go to profile, open info tab. Now type in the player ID number of your main account.

You will then open up your main account on mobile.

i  can  access  my  main  account  on  MacBook.    The  problem  is  that  when  I  enter  the  same  Plarium  ID  and  password  in  my  new  account  on  iphone  12 ,  I  remain with  the  newly  created  character  and  no  opportunity  to  change  um12345678  l  12346678  credentials.

I honestly am unsure how to fix this. I'm not an apple user at all. I know you can log out of the new account in the menus after clicking your PfP. Then you should be able to log back in with the old account.

If that doesn't work, maybe open a Support Ticket 

You need to change your new account id to your main accounts id. You can do that in the player profile window. I had no truble doing it on bluestacks

I hope this works for them! Thx for the assist. :)