Not to Mess Up by Replacing Relationship with Different Primery Ke

Hi Guys!

I have a questions. In my database there is a field called customer id. it
is present in two tables and used to build a relationship one -many between
them. A field type is number so you have to enter it manually. I messed up as
I added a number outside the numeric sequence and followed it up. So instead
of 89, I added 99. I want to correct it by adding a new field with
autonumber. In this way, I would not mess up as my database creates new
numbers for me. However, I am a bit afraid that by adding a new field and
changing relationship I will destroy the balance between tables and make
wrong records joined. How can I avoid it??

Thank you for your time and help

Anna