You can't store to 2 tables directly, what you can do is either

• Create second field with different storage, than use computation to copy value from first field when it is filled
• Insert data yourself using onBeforeStore or on AfterStore plugins from Code pack

I've done it I wonder if there is a way without that I need to create another field may be using PHP but would like a tutorial

There is another way - use SD live plugin for second field, but I would not know of any method to store value to 2 tables using jsut one field.

To use onBeforeStore or onAfterStoree there is no tutorial for this, you need to know joomla&php programming to use them, this might help

https://docs.joomla.org/Inserting,_Updating_and_Removing_data_using_JDatabase

Note: in my answer above "than use computation to copy" should be "than use conditionals to copy"

You could also concatenate it, just this one field, and choose your storage. I don't know if you can store in any table I assume you can.